Merge branch 'codex/mail-categories-v1'

Wino.Core.Domain/Entities/Mail/MailCategory.cs

@@ -0,0 +1,25 @@
+using System;
+using SQLite;
+using Wino.Core.Domain.Enums;
+
+namespace Wino.Core.Domain.Entities.Mail;
+
+public class MailCategory
+{
+    [PrimaryKey]
+    public Guid Id { get; set; }
+
+    public Guid MailAccountId { get; set; }
+
+    public string RemoteId { get; set; }
+
+    public string Name { get; set; }
+
+    public bool IsFavorite { get; set; }
+
+    public string BackgroundColorHex { get; set; }
+
+    public string TextColorHex { get; set; }
+
+    public MailCategorySource Source { get; set; } = MailCategorySource.Local;
+}

Wino.Core.Domain/Entities/Mail/MailCategoryAssignment.cs

@@ -0,0 +1,14 @@
+using System;
+using SQLite;
+
+namespace Wino.Core.Domain.Entities.Mail;
+
+public class MailCategoryAssignment
+{
+    [PrimaryKey]
+    public Guid Id { get; set; }
+
+    public Guid MailCategoryId { get; set; }
+
+    public Guid MailCopyUniqueId { get; set; }
+}

Wino.Core.Domain/Entities/Shared/MailAccount.cs

@@ -132,5 +132,10 @@ public class MailAccount
     /// </summary>
     public bool IsAliasSyncSupported => ProviderType == MailProviderType.Gmail || ProviderType == MailProviderType.Outlook;
 
+    /// <summary>
+    /// Gets whether the account can perform category definition sync type.
+    /// </summary>
+    public bool IsCategorySyncSupported => ProviderType == MailProviderType.Outlook;
+
     public override string ToString() => Name;
 }

Wino.Core.Domain/Enums/MailCategorySource.cs

@@ -0,0 +1,7 @@
+namespace Wino.Core.Domain.Enums;
+
+public enum MailCategorySource
+{
+    Local,
+    Outlook
+}

Wino.Core.Domain/Enums/MailOperation.cs

@@ -13,6 +13,7 @@ public enum MailSynchronizerOperation
     AlwaysMoveTo,
     MoveToFocused,
     Archive,
+    UpdateCategories,
 }
 
 public enum FolderSynchronizerOperation
@@ -35,6 +36,13 @@ public enum CalendarSynchronizerOperation
     TentativeEvent,
 }
 
+public enum CategorySynchronizerOperation
+{
+    CreateCategory,
+    UpdateCategory,
+    DeleteCategory,
+}
+
 // UI requests
 public enum MailOperation
 {

Wino.Core.Domain/Enums/MailSynchronizationType.cs

@@ -3,6 +3,7 @@
 public enum MailSynchronizationType
 {
     UpdateProfile, // Only update profile information
+    Categories, // Only update mail categories
     ExecuteRequests, // Run the queued requests, and then synchronize if needed.
     FoldersOnly, // Only synchronize folder metadata.
     InboxOnly, // Only Inbox, Sent, Draft and Deleted folders.

Wino.Core.Domain/Enums/WinoPage.cs

@@ -24,6 +24,7 @@ public enum WinoPage
     AppPreferencesPage,
     SettingOptionsPage,
     AliasManagementPage,
+    MailCategoryManagementPage,
     ImapCalDavSettingsPage,
     KeyboardShortcutsPage,
     CalendarPage,

Wino.Core.Domain/Interfaces/IFolderMenuItem.cs

@@ -14,6 +14,22 @@ public interface IFolderMenuItem : IBaseFolderMenuItem
 
 public interface IMergedAccountFolderMenuItem : IBaseFolderMenuItem { }
 
+public interface IMailCategoryMenuItem : IBaseFolderMenuItem
+{
+    Entities.Mail.MailCategory MailCategory { get; }
+    string TextColorHex { get; }
+    string BackgroundColorHex { get; }
+    bool HasTextColor { get; }
+}
+
+public interface IMergedMailCategoryMenuItem : IBaseFolderMenuItem
+{
+    IReadOnlyList<Entities.Mail.MailCategory> Categories { get; }
+    string TextColorHex { get; }
+    string BackgroundColorHex { get; }
+    bool HasTextColor { get; }
+}
+
 public interface IBaseFolderMenuItem : IMenuItem
 {
     string FolderName { get; }

Wino.Core.Domain/Interfaces/IMailCategoryService.cs

@@ -0,0 +1,30 @@
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Wino.Core.Domain.Entities.Mail;
+using Wino.Core.Domain.Models.Accounts;
+
+namespace Wino.Core.Domain.Interfaces;
+
+public interface IMailCategoryService
+{
+    Task<List<MailCategory>> GetCategoriesAsync(Guid accountId);
+    Task<List<MailCategory>> GetFavoriteCategoriesAsync(Guid accountId);
+    Task<MailCategory> GetCategoryAsync(Guid categoryId);
+    Task<bool> CategoryNameExistsAsync(Guid accountId, string name, Guid? excludedCategoryId = null);
+    Task<MailCategory> CreateCategoryAsync(MailCategory category);
+    Task UpdateCategoryAsync(MailCategory category);
+    Task DeleteCategoryAsync(Guid categoryId);
+    Task DeleteCategoriesAsync(Guid accountId);
+    Task ToggleFavoriteAsync(Guid categoryId, bool isFavorite);
+    Task UpdateRemoteIdAsync(Guid categoryId, string remoteId);
+    Task ReplaceCategoriesAsync(Guid accountId, IEnumerable<MailCategory> categories);
+    Task ReplaceMailAssignmentsAsync(Guid accountId, Guid mailCopyUniqueId, IEnumerable<string> categoryNames);
+    Task AssignCategoryAsync(Guid categoryId, IEnumerable<Guid> mailCopyUniqueIds);
+    Task UnassignCategoryAsync(Guid categoryId, IEnumerable<Guid> mailCopyUniqueIds);
+    Task<List<MailCategory>> GetCategoriesForMailAsync(Guid accountId, IEnumerable<Guid> mailCopyUniqueIds);
+    Task<List<Guid>> GetAssignedCategoryIdsForAllAsync(IEnumerable<Guid> mailCopyUniqueIds);
+    Task<List<string>> GetCategoryNamesForMailAsync(Guid mailCopyUniqueId);
+    Task<List<MailCopy>> GetMailCopiesForCategoryAsync(Guid categoryId);
+    Task<List<UnreadCategoryCountResult>> GetUnreadCategoryCountResultsAsync(IEnumerable<Guid> accountIds);
+}

Wino.Core.Domain/Interfaces/IMailDialogService.cs

@@ -11,6 +11,7 @@ using Wino.Core.Domain.Models;
 using Wino.Core.Domain.Models.Accounts;
 using Wino.Core.Domain.Models.Calendar;
 using Wino.Core.Domain.Models.Folders;
+using Wino.Core.Domain.Models.MailItem;
 
 namespace Wino.Core.Domain.Interfaces;
 
@@ -52,6 +53,13 @@ public interface IMailDialogService : IDialogServiceBase
     /// <returns>Created alias model if not canceled.</returns>
     Task<ICreateAccountAliasDialog> ShowCreateAccountAliasDialogAsync();
 
+    /// <summary>
+    /// Presents a dialog to the user for mail category creation/modification.
+    /// </summary>
+#pragma warning disable CS8625
+    Task<MailCategoryDialogResult> ShowEditMailCategoryDialogAsync(MailCategory category = null);
+#pragma warning restore CS8625
+
     /// <summary>
     /// Presents a dialog to the user to show email source.
     /// </summary>

Wino.Core.Domain/Interfaces/IRequestBundle.cs

@@ -72,3 +72,9 @@ public interface ICalendarActionRequest : IRequestBase
     Guid? LocalCalendarItemId { get; }
     CalendarSynchronizerOperation Operation { get; }
 }
+
+public interface ICategoryActionRequest : IRequestBase
+{
+    Guid AccountId { get; }
+    CategorySynchronizerOperation Operation { get; }
+}

Wino.Core.Domain/Interfaces/ISynchronizationManager.cs

@@ -63,6 +63,12 @@ public interface ISynchronizationManager
     Task<MailSynchronizationResult> SynchronizeAliasesAsync(Guid accountId,
                                                             CancellationToken cancellationToken = default);
 
+    /// <summary>
+    /// Handles category synchronization for the given account.
+    /// </summary>
+    Task<MailSynchronizationResult> SynchronizeCategoriesAsync(Guid accountId,
+                                                               CancellationToken cancellationToken = default);
+
     /// <summary>
     /// Handles profile synchronization for the given account.
     /// </summary>

Wino.Core.Domain/Interfaces/IWinoRequestDelegator.cs

@@ -1,4 +1,6 @@
-using System.Threading.Tasks;
+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
 using Wino.Core.Domain.Models.Calendar;
 using Wino.Core.Domain.Models.Folders;
 using Wino.Core.Domain.Models.MailItem;
@@ -36,4 +38,9 @@ public interface IWinoRequestDelegator
     /// </summary>
     /// <param name="calendarOperationPreparationRequest">Calendar preparation request.</param>
     Task ExecuteAsync(CalendarOperationPreparationRequest calendarOperationPreparationRequest);
+
+    /// <summary>
+    /// Queues pre-built requests for a single account and triggers synchronization.
+    /// </summary>
+    Task ExecuteAsync(Guid accountId, IEnumerable<IRequestBase> requests);
 }

Wino.Core.Domain/MenuItems/MailCategoryMenuItem.cs

@@ -0,0 +1,48 @@
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Linq;
+using CommunityToolkit.Mvvm.ComponentModel;
+using Wino.Core.Domain.Entities.Mail;
+using Wino.Core.Domain.Entities.Shared;
+using Wino.Core.Domain.Enums;
+using Wino.Core.Domain.Interfaces;
+using Wino.Core.Domain.Models.Folders;
+
+namespace Wino.Core.Domain.MenuItems;
+
+public partial class MailCategoryMenuItem : MenuItemBase<MailCategory, IMenuItem>, IFolderMenuItem, IMailCategoryMenuItem
+{
+    private IReadOnlyList<IMailItemFolder> _handlingFolders;
+
+    [ObservableProperty]
+    private int unreadItemCount;
+
+    public MailCategoryMenuItem(MailCategory category, MailAccount parentAccount, IEnumerable<IMailItemFolder> handlingFolders, IMenuItem parentMenuItem)
+        : base(category, category.Id, parentMenuItem)
+    {
+        ParentAccount = parentAccount;
+        _handlingFolders = handlingFolders?.ToList() ?? [];
+    }
+
+    public string FolderName => Parameter.Name;
+    public bool IsSynchronizationEnabled => false;
+    public SpecialFolderType SpecialFolderType => SpecialFolderType.Other;
+    public IEnumerable<IMailItemFolder> HandlingFolders => _handlingFolders;
+    public new ObservableCollection<IMenuItem> SubMenuItems { get; } = [];
+    public bool IsMoveTarget => true;
+    public bool IsSticky => false;
+    public bool IsSystemFolder => false;
+    public bool ShowUnreadCount => true;
+    public string AssignedAccountName => ParentAccount?.Name;
+    public MailAccount ParentAccount { get; private set; }
+    public string TextColorHex => Parameter.TextColorHex;
+    public string BackgroundColorHex => Parameter.BackgroundColorHex;
+    public bool HasTextColor => !string.IsNullOrWhiteSpace(Parameter.TextColorHex);
+    public MailCategory MailCategory => Parameter;
+
+    public void UpdateFolder(IMailItemFolder folder)
+    {
+    }
+
+    public void UpdateParentAccounnt(MailAccount account) => ParentAccount = account;
+}

Wino.Core.Domain/MenuItems/MenuItemCollection.cs

@@ -22,11 +22,13 @@ public class MenuItemCollection : ObservableRangeCollection<IMenuItem>
 
     public IEnumerable<IAccountMenuItem> GetAllAccountMenuItems()
     {
-        foreach (var item in this)
+        var rootItems = this.ToList();
+
+        foreach (var item in rootItems)
         {
             if (item is MergedAccountMenuItem mergedAccountMenuItem)
             {
-                foreach (var singleItem in mergedAccountMenuItem.SubMenuItems.OfType<IAccountMenuItem>())
+                foreach (var singleItem in mergedAccountMenuItem.SubMenuItems.OfType<IAccountMenuItem>().ToList())
                 {
                     yield return singleItem;
                 }
@@ -40,9 +42,11 @@ public class MenuItemCollection : ObservableRangeCollection<IMenuItem>
 
     public IEnumerable<IBaseFolderMenuItem> GetAllFolderMenuItems(Guid folderId)
     {
-        foreach (var item in this)
+        var rootItems = this.ToList();
+
+        foreach (var item in rootItems)
         {
-            if (item is IBaseFolderMenuItem folderMenuItem)
+            if (item is IBaseFolderMenuItem folderMenuItem && item is not IMailCategoryMenuItem && item is not IMergedMailCategoryMenuItem)
             {
                 if (folderMenuItem.HandlingFolders.Any(a => a.Id == folderId))
                 {
@@ -50,7 +54,7 @@ public class MenuItemCollection : ObservableRangeCollection<IMenuItem>
                 }
                 else if (folderMenuItem.SubMenuItems.Any())
                 {
-                    foreach (var subItem in folderMenuItem.SubMenuItems.OfType<IBaseFolderMenuItem>())
+                    foreach (var subItem in folderMenuItem.SubMenuItems.OfType<IBaseFolderMenuItem>().ToList())
                     {
                         if (subItem.HandlingFolders.Any(a => a.Id == folderId))
                         {
@@ -65,8 +69,10 @@ public class MenuItemCollection : ObservableRangeCollection<IMenuItem>
 
     public bool TryGetAccountMenuItem(Guid accountId, out IAccountMenuItem value)
     {
-        value = this.OfType<AccountMenuItem>().FirstOrDefault(a => a.AccountId == accountId);
+        var rootItems = this.ToList();
-        value ??= this.OfType<MergedAccountMenuItem>().FirstOrDefault(a => a.SubMenuItems.OfType<AccountMenuItem>().Where(b => b.AccountId == accountId) != null);
+
+        value = rootItems.OfType<AccountMenuItem>().FirstOrDefault(a => a.AccountId == accountId);
+        value ??= rootItems.OfType<MergedAccountMenuItem>().FirstOrDefault(a => a.SubMenuItems.OfType<AccountMenuItem>().Any(b => b.AccountId == accountId));
 
         return value != null;
     }
@@ -74,7 +80,9 @@ public class MenuItemCollection : ObservableRangeCollection<IMenuItem>
     // Pattern: Look for special folder menu item inside the loaded folders for Windows Mail style menu items.
     public bool TryGetWindowsStyleRootSpecialFolderMenuItem(Guid accountId, SpecialFolderType specialFolderType, out FolderMenuItem value)
     {
-        value = this.OfType<IBaseFolderMenuItem>()
+        var rootItems = this.ToList();
+
+        value = rootItems.OfType<IBaseFolderMenuItem>()
                 .FirstOrDefault(a => a.HandlingFolders.Any(b => b.MailAccountId == accountId && b.SpecialFolderType == specialFolderType)) as FolderMenuItem;
 
         return value != null;
@@ -84,7 +92,9 @@ public class MenuItemCollection : ObservableRangeCollection<IMenuItem>
     // This will not look for the folders inside individual account menu items inside merged account menu item.
     public bool TryGetMergedAccountSpecialFolderMenuItem(Guid mergedInboxId, SpecialFolderType specialFolderType, out IBaseFolderMenuItem value)
     {
-        value = this.OfType<MergedAccountFolderMenuItem>()
+        var rootItems = this.ToList();
+
+        value = rootItems.OfType<MergedAccountFolderMenuItem>()
                 .Where(a => a.MergedInbox.Id == mergedInboxId)
                 .FirstOrDefault(a => a.SpecialFolderType == specialFolderType);
 
@@ -93,11 +103,14 @@ public class MenuItemCollection : ObservableRangeCollection<IMenuItem>
 
     public bool TryGetFolderMenuItem(Guid folderId, out IBaseFolderMenuItem value)
     {
+        var rootItems = this.ToList();
+
         // Root folders
-        value = this.OfType<IBaseFolderMenuItem>()
+        value = rootItems.OfType<IBaseFolderMenuItem>()
+                .Where(a => a is not IMailCategoryMenuItem && a is not IMergedMailCategoryMenuItem)
                 .FirstOrDefault(a => a.HandlingFolders.Any(b => b.Id == folderId));
 
-        value ??= this.OfType<FolderMenuItem>()
+        value ??= rootItems.OfType<FolderMenuItem>()
             .SelectMany(a => a.SubMenuItems)
                 .OfType<IBaseFolderMenuItem>()
                 .FirstOrDefault(a => a.HandlingFolders.Any(b => b.Id == folderId));
@@ -105,10 +118,23 @@ public class MenuItemCollection : ObservableRangeCollection<IMenuItem>
         return value != null;
     }
 
+    public bool TryGetCategoryMenuItem(Guid categoryId, out IBaseFolderMenuItem value)
+    {
+        var rootItems = this.ToList();
+
+        value = rootItems.OfType<IMailCategoryMenuItem>()
+            .FirstOrDefault(a => a.MailCategory.Id == categoryId);
+
+        value ??= rootItems.OfType<IMergedMailCategoryMenuItem>()
+            .FirstOrDefault(a => a.Categories.Any(b => b.Id == categoryId)) as IBaseFolderMenuItem;
+
+        return value != null;
+    }
+
     public void UpdateUnreadItemCountsToZero()
     {
         // Handle the root folders.
-        foreach (var item in this.OfType<IBaseFolderMenuItem>())
+        foreach (var item in this.OfType<IBaseFolderMenuItem>().ToList())
         {
             RecursivelyResetUnreadItemCount(item);
         }
@@ -120,7 +146,7 @@ public class MenuItemCollection : ObservableRangeCollection<IMenuItem>
 
         if (baseFolderMenuItem.SubMenuItems == null) return;
 
-        foreach (var subMenuItem in baseFolderMenuItem.SubMenuItems.OfType<IBaseFolderMenuItem>())
+        foreach (var subMenuItem in baseFolderMenuItem.SubMenuItems.OfType<IBaseFolderMenuItem>().ToList())
         {
             RecursivelyResetUnreadItemCount(subMenuItem);
         }
@@ -128,7 +154,9 @@ public class MenuItemCollection : ObservableRangeCollection<IMenuItem>
 
     public bool TryGetSpecialFolderMenuItem(Guid accountId, SpecialFolderType specialFolderType, out FolderMenuItem value)
     {
-        value = this.OfType<IBaseFolderMenuItem>()
+        var rootItems = this.ToList();
+
+        value = rootItems.OfType<IBaseFolderMenuItem>()
                 .FirstOrDefault(a => a.HandlingFolders.Any(b => b.MailAccountId == accountId && b.SpecialFolderType == specialFolderType)) as FolderMenuItem;
 
         return value != null;
@@ -142,11 +170,12 @@ public class MenuItemCollection : ObservableRangeCollection<IMenuItem>
     public AccountMenuItem GetSpecificAccountMenuItem(Guid accountId)
     {
         AccountMenuItem accountMenuItem = null;
+        var rootItems = this.ToList();
 
-        accountMenuItem = this.OfType<AccountMenuItem>().FirstOrDefault(a => a.HoldingAccounts.Any(b => b.Id == accountId));
+        accountMenuItem = rootItems.OfType<AccountMenuItem>().FirstOrDefault(a => a.HoldingAccounts.Any(b => b.Id == accountId));
 
         // Look for the items inside the merged accounts if regular menu item is not found.
-        accountMenuItem ??= this.OfType<MergedAccountMenuItem>()
+        accountMenuItem ??= rootItems.OfType<MergedAccountMenuItem>()
             .FirstOrDefault(a => a.HoldingAccounts.Any(b => b.Id == accountId))?.SubMenuItems
             .OfType<AccountMenuItem>()
             .FirstOrDefault(a => a.AccountId == accountId);
@@ -167,7 +196,7 @@ public class MenuItemCollection : ObservableRangeCollection<IMenuItem>
     /// <param name="isEnabled">Whether menu items should be enabled or disabled.</param>
     public async Task SetAccountMenuItemEnabledStatusAsync(bool isEnabled)
     {
-        var accountItems = this.Where(a => a is IAccountMenuItem).Cast<IAccountMenuItem>();
+        var accountItems = this.Where(a => a is IAccountMenuItem).Cast<IAccountMenuItem>().ToList();
 
         await _dispatcher.ExecuteOnUIThread(() =>
         {
@@ -192,6 +221,7 @@ public class MenuItemCollection : ObservableRangeCollection<IMenuItem>
     {
         // Check root-level items.
         var rootItem = this.OfType<IBaseFolderMenuItem>()
+            .Where(a => a is not IMailCategoryMenuItem && a is not IMergedMailCategoryMenuItem)
             .FirstOrDefault(a => a.HandlingFolders.Any(b => b.Id == folderId));
 
         if (rootItem != null)
@@ -201,7 +231,7 @@ public class MenuItemCollection : ObservableRangeCollection<IMenuItem>
         }
 
         // Check sub-items of root folders.
-        foreach (var rootFolder in this.OfType<IBaseFolderMenuItem>())
+        foreach (var rootFolder in this.OfType<IBaseFolderMenuItem>().ToList())
         {
             var subItem = rootFolder.SubMenuItems
                 .OfType<IBaseFolderMenuItem>()

Wino.Core.Domain/MenuItems/MergedMailCategoryMenuItem.cs

@@ -0,0 +1,44 @@
+using System.Collections.Generic;
+using System.Linq;
+using CommunityToolkit.Mvvm.ComponentModel;
+using Wino.Core.Domain.Entities.Mail;
+using Wino.Core.Domain.Entities.Shared;
+using Wino.Core.Domain.Enums;
+using Wino.Core.Domain.Interfaces;
+using Wino.Core.Domain.Models.Folders;
+
+namespace Wino.Core.Domain.MenuItems;
+
+public partial class MergedMailCategoryMenuItem : MenuItemBase<List<MailCategory>, IMenuItem>, IMergedAccountFolderMenuItem, IMergedMailCategoryMenuItem
+{
+    private readonly IReadOnlyList<IMailItemFolder> _handlingFolders;
+
+    [ObservableProperty]
+    private int unreadItemCount;
+
+    public MergedMailCategoryMenuItem(List<MailCategory> categories, IEnumerable<IMailItemFolder> handlingFolders, MergedInbox mergedInbox)
+        : base(categories, null, null)
+    {
+        _handlingFolders = handlingFolders?.ToList() ?? [];
+        MergedInbox = mergedInbox;
+    }
+
+    public string FolderName => Parameter.FirstOrDefault()?.Name ?? string.Empty;
+    public bool IsSynchronizationEnabled => false;
+    public SpecialFolderType SpecialFolderType => SpecialFolderType.Other;
+    public IEnumerable<IMailItemFolder> HandlingFolders => _handlingFolders;
+    public bool IsMoveTarget => true;
+    public bool IsSticky => false;
+    public bool IsSystemFolder => false;
+    public bool ShowUnreadCount => true;
+    public string AssignedAccountName => MergedInbox?.Name;
+    public MergedInbox MergedInbox { get; }
+    public string TextColorHex => Parameter.FirstOrDefault()?.TextColorHex;
+    public string BackgroundColorHex => Parameter.FirstOrDefault()?.BackgroundColorHex;
+    public bool HasTextColor => !string.IsNullOrWhiteSpace(TextColorHex);
+    public IReadOnlyList<MailCategory> Categories => Parameter;
+
+    public void UpdateFolder(IMailItemFolder folder)
+    {
+    }
+}

Wino.Core.Domain/Models/Accounts/UnreadCategoryCountResult.cs

@@ -0,0 +1,10 @@
+using System;
+
+namespace Wino.Core.Domain.Models.Accounts;
+
+public class UnreadCategoryCountResult
+{
+    public Guid CategoryId { get; set; }
+    public Guid AccountId { get; set; }
+    public int UnreadItemCount { get; set; }
+}

Wino.Core.Domain/Models/MailItem/MailCategoryColorOption.cs

@@ -0,0 +1,3 @@
+namespace Wino.Core.Domain.Models.MailItem;
+
+public sealed record MailCategoryColorOption(string BackgroundColorHex, string TextColorHex);

Wino.Core.Domain/Models/MailItem/MailCategoryDialogResult.cs

@@ -0,0 +1,3 @@
+namespace Wino.Core.Domain.Models.MailItem;
+
+public sealed record MailCategoryDialogResult(string Name, string BackgroundColorHex, string TextColorHex);

Wino.Core.Domain/Models/MailItem/MailCategoryPalette.cs

@@ -0,0 +1,30 @@
+using System.Collections.Generic;
+
+namespace Wino.Core.Domain.Models.MailItem;
+
+public static class MailCategoryPalette
+{
+    public static IReadOnlyList<MailCategoryColorOption> DefaultOptions { get; } =
+    [
+        new("#FEE2E2", "#991B1B"),
+        new("#FECACA", "#7F1D1D"),
+        new("#FFEDD5", "#9A3412"),
+        new("#FED7AA", "#7C2D12"),
+        new("#FEF3C7", "#92400E"),
+        new("#FDE68A", "#78350F"),
+        new("#ECFCCB", "#3F6212"),
+        new("#D9F99D", "#365314"),
+        new("#DCFCE7", "#166534"),
+        new("#BBF7D0", "#14532D"),
+        new("#CCFBF1", "#115E59"),
+        new("#99F6E4", "#134E4A"),
+        new("#CFFAFE", "#155E75"),
+        new("#A5F3FC", "#164E63"),
+        new("#DBEAFE", "#1D4ED8"),
+        new("#BFDBFE", "#1E3A8A"),
+        new("#E0E7FF", "#4338CA"),
+        new("#DDD6FE", "#5B21B6"),
+        new("#F3E8FF", "#7E22CE"),
+        new("#FCE7F3", "#9D174D")
+    ];
+}

Wino.Core.Domain/Models/MailItem/MailInsertPackage.cs

@@ -9,4 +9,5 @@ public record NewMailItemPackage(
     MailCopy Copy,
     MimeMessage Mime,
     string AssignedRemoteFolderId,
-    IReadOnlyList<AccountContact> ExtractedContacts = null);
+    IReadOnlyList<AccountContact> ExtractedContacts = null,
+    IReadOnlyList<string> CategoryNames = null);

Wino.Core.Domain/Models/MailItem/MailListInitializationOptions.cs

@@ -17,4 +17,8 @@ public record MailListInitializationOptions(IEnumerable<IMailItemFolder> Folders
                                             List<MailCopy> PreFetchMailCopies = null,
                                             bool DeduplicateByServerId = false,
                                             int Skip = 0,
-                                            int Take = 0);
+                                            int Take = 0)
+{
+    public IReadOnlyList<Guid> CategoryIds { get; init; }
+    public bool IsCategoryView => CategoryIds?.Count > 0;
+}

Wino.Core.Domain/Models/Requests/RequestBase.cs

@@ -35,6 +35,10 @@ public abstract record CalendarRequestBase(CalendarItem Item) : RequestBase<Cale
     public virtual Guid? LocalCalendarItemId => Item?.Id;
 }
 
+public abstract record CategoryRequestBase(Guid AccountId) : RequestBase<CategorySynchronizerOperation>, ICategoryActionRequest
+{
+}
+
 public class BatchCollection<TRequestType> : List<TRequestType>, IUIChangeRequest where TRequestType : IUIChangeRequest
 {
     public BatchCollection(IEnumerable<TRequestType> collection) : base(collection)

Wino.Core.Domain/Models/Settings/SettingsNavigationItemInfo.cs

@@ -170,6 +170,7 @@ public static class SettingsNavigationInfoProvider
             WinoPage.AccountDetailsPage => WinoPage.ManageAccountsPage,
             WinoPage.MergedAccountDetailsPage => WinoPage.ManageAccountsPage,
             WinoPage.AliasManagementPage => WinoPage.ManageAccountsPage,
+            WinoPage.MailCategoryManagementPage => WinoPage.ManageAccountsPage,
             WinoPage.SignatureManagementPage => WinoPage.ManageAccountsPage,
             WinoPage.ImapCalDavSettingsPage => WinoPage.ManageAccountsPage,
             WinoPage.CreateEmailTemplatePage => WinoPage.EmailTemplatesPage,

Wino.Core.Domain/Translations/en_US/resources.json

@@ -67,6 +67,7 @@
     "BasicIMAPSetupDialog_Password": "Password",
     "BasicIMAPSetupDialog_Title": "IMAP Account",
     "Busy": "Busy",
+    "Buttons_Add": "Add",
     "Buttons_AddAccount": "Add Account",
     "Buttons_FixAccount": "Fix Account",
     "Buttons_AddNewAlias": "Add New Alias",
@@ -877,10 +878,28 @@
     "SettingsManageAccountSettings_Title": "Manage Accounts",
     "SettingsManageAliases_Description": "See e-mail aliases assigned for this account, update or delete them.",
     "SettingsManageAliases_Title": "Aliases",
+    "SettingsMailCategories_Description": "Manage synchronized and local categories for this account.",
+    "SettingsMailCategories_Title": "Categories",
     "SettingsEditAccountDetails_Title": "Edit Account Details",
     "SettingsEditAccountDetails_Description": "Change account name, sender name and assign a new color if you like.",
     "EditAccountDetailsPage_SaveSuccess_Title": "Changes Saved",
     "EditAccountDetailsPage_SaveSuccess_Message": "Your account details have been updated successfully.",
+    "MailCategoryManagementPage_Title": "Categories",
+    "MailCategoryManagementPage_Description": "Create, edit, delete, and favorite categories for this account.",
+    "MailCategoryManagementPage_Empty": "No categories yet.",
+    "MailCategoryManagementPage_DeleteConfirmationTitle": "Delete Category",
+    "MailCategoryManagementPage_DeleteConfirmationMessage": "Delete category \"{0}\"?",
+    "MailCategoryManagementPage_RefreshConfirmationMessage": "This will delete all your local categories, and re-synchronize everything from the server. Do you want to continue?",
+    "MailCategoryMenuItem": "Category",
+    "MailCategoryDialog_CreateTitle": "Create category",
+    "MailCategoryDialog_EditTitle": "Edit category",
+    "MailCategoryDialog_Name": "Name",
+    "MailCategoryDialog_NamePlaceholder": "Category name",
+    "MailCategoryDialog_Color": "Color",
+    "MailCategoryDialog_InvalidNameTitle": "Category name required",
+    "MailCategoryDialog_InvalidNameMessage": "Enter a category name to continue.",
+    "MailCategoryDialog_DuplicateTitle": "Category already exists",
+    "MailCategoryDialog_DuplicateMessage": "A category with the same name already exists for this account.",
     "SettingsManageLink_Description": "Move items to add new link or remove existing link.",
     "SettingsManageLink_Title": "Manage Link",
     "SettingsMarkAsRead_Description": "Change what should happen to the selected item.",
@@ -1493,11 +1512,13 @@
     "AccountSetup_Step_TestingCalendarAuth": "Testing calendar authentication",
     "AccountSetup_Step_SavingAccount": "Saving account information",
     "AccountSetup_Step_FetchingCalendarMetadata": "Fetching calendar metadata",
+    "AccountSetup_Step_SyncingCategories": "Synchronizing categories",
     "AccountSetup_Step_SyncingAliases": "Synchronizing aliases",
     "AccountSetup_Step_Finalizing": "Finalizing setup",
     "AccountSetup_FailureMessage": "Setup failed. Go back to fix your settings, or try again later.",
     "AccountSetup_SuccessMessage": "Your account has been set up successfully!",
     "AccountSetup_GoBackButton": "Go Back",
     "AccountSetup_TryAgainButton": "Try Again",
+    "Exception_FailedToSynchronizeCategories": "Failed to synchronize categories",
     "ImapCalDavSettings_AutoDiscoveryFailed": "Auto-discovery failed. Please enter settings manually in the Advanced tab."
 }

Wino.Core.Tests/Services/MailFetchingTests.cs

@@ -510,7 +510,8 @@ public class MailFetchingTests : IAsyncLifetime
             preferencesService.Object,
             contactPictureFileService.Object);
 
-        var folderService = new FolderService(db, accountService);
+        var mailCategoryService = new MailCategoryService(db);
+        var folderService = new FolderService(db, accountService, mailCategoryService);
         var contactService = new ContactService(db);
         var sentMailReceiptService = new SentMailReceiptService(db, folderService, accountService);
 
@@ -522,6 +523,7 @@ public class MailFetchingTests : IAsyncLifetime
             signatureService.Object,
             mimeFileService.Object,
             preferencesService.Object,
-            sentMailReceiptService);
+            sentMailReceiptService,
+            mailCategoryService);
     }
 }

Wino.Core.Tests/Services/MailThreadingTests.cs

@@ -269,7 +269,8 @@ public class MailThreadingTests : IAsyncLifetime
             preferencesService.Object,
             contactPictureFileService.Object);
 
-        var folderService = new FolderService(db, accountService);
+        var mailCategoryService = new MailCategoryService(db);
+        var folderService = new FolderService(db, accountService, mailCategoryService);
         var contactService = new ContactService(db);
         var sentMailReceiptService = new SentMailReceiptService(db, folderService, accountService);
 
@@ -281,6 +282,7 @@ public class MailThreadingTests : IAsyncLifetime
             signatureService.Object,
             mimeFileService.Object,
             preferencesService.Object,
-            sentMailReceiptService);
+            sentMailReceiptService,
+            mailCategoryService);
     }
 }

Wino.Core.Tests/Synchronizers/OutlookSynchronizerRequestSuccessTests.cs

@@ -70,8 +70,9 @@ public sealed class OutlookSynchronizerRequestSuccessTests
 
         var authenticator = new Mock<IAuthenticator>(MockBehavior.Loose);
         var errorFactory = new Mock<IOutlookSynchronizerErrorHandlerFactory>(MockBehavior.Loose);
+        var mailCategoryService = new Mock<IMailCategoryService>(MockBehavior.Loose);
 
-        return new OutlookSynchronizer(account, authenticator.Object, changeProcessor, errorFactory.Object);
+        return new OutlookSynchronizer(account, authenticator.Object, changeProcessor, errorFactory.Object, mailCategoryService.Object);
     }
 
     private static MailCopy CreateMailCopy() =>

Wino.Core/Requests/Category/MailCategoryCreateRequest.cs

@@ -0,0 +1,10 @@
+using Wino.Core.Domain.Entities.Mail;
+using Wino.Core.Domain.Enums;
+using Wino.Core.Domain.Models.Requests;
+
+namespace Wino.Core.Requests.Category;
+
+public record MailCategoryCreateRequest(MailCategory Category) : CategoryRequestBase(Category.MailAccountId)
+{
+    public override CategorySynchronizerOperation Operation => CategorySynchronizerOperation.CreateCategory;
+}

Wino.Core/Requests/Category/MailCategoryDeleteRequest.cs

@@ -0,0 +1,14 @@
+using System.Collections.Generic;
+using Wino.Core.Domain.Entities.Mail;
+using Wino.Core.Domain.Enums;
+using Wino.Core.Domain.Models.Requests;
+
+namespace Wino.Core.Requests.Category;
+
+public record MailCategoryDeleteRequest(
+    MailCategory Category,
+    string PreviousRemoteId,
+    IReadOnlyList<MailCategoryMessageUpdateTarget> AffectedMessages = null) : CategoryRequestBase(Category.MailAccountId)
+{
+    public override CategorySynchronizerOperation Operation => CategorySynchronizerOperation.DeleteCategory;
+}

Wino.Core/Requests/Category/MailCategoryRequestModels.cs

@@ -0,0 +1,5 @@
+using System.Collections.Generic;
+
+namespace Wino.Core.Requests.Category;
+
+public sealed record MailCategoryMessageUpdateTarget(string MessageId, IReadOnlyList<string> CategoryNames);

Wino.Core/Requests/Category/MailCategoryUpdateRequest.cs

@@ -0,0 +1,15 @@
+using System.Collections.Generic;
+using Wino.Core.Domain.Entities.Mail;
+using Wino.Core.Domain.Enums;
+using Wino.Core.Domain.Models.Requests;
+
+namespace Wino.Core.Requests.Category;
+
+public record MailCategoryUpdateRequest(
+    MailCategory Category,
+    string PreviousName,
+    string PreviousRemoteId,
+    IReadOnlyList<MailCategoryMessageUpdateTarget> AffectedMessages = null) : CategoryRequestBase(Category.MailAccountId)
+{
+    public override CategorySynchronizerOperation Operation => CategorySynchronizerOperation.UpdateCategory;
+}

Wino.Core/Requests/Mail/MailCategoryAssignmentRequest.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using Wino.Core.Domain.Entities.Mail;
+using Wino.Core.Domain.Enums;
+using Wino.Core.Domain.Interfaces;
+using Wino.Core.Domain.Models.Requests;
+
+namespace Wino.Core.Requests.Mail;
+
+public record MailCategoryAssignmentRequest(
+    MailCopy Item,
+    Guid MailCategoryId,
+    string CategoryName,
+    IReadOnlyList<string> CategoryNames,
+    bool IsAssigned) : MailRequestBase(Item), ICustomFolderSynchronizationRequest
+{
+    public override MailSynchronizerOperation Operation => MailSynchronizerOperation.UpdateCategories;
+    public List<Guid> SynchronizationFolderIds => [Item.FolderId];
+    public bool ExcludeMustHaveFolders => true;
+}
+
+public class BatchMailCategoryAssignmentRequest : BatchCollection<MailCategoryAssignmentRequest>
+{
+    public BatchMailCategoryAssignmentRequest(IEnumerable<MailCategoryAssignmentRequest> collection) : base(collection)
+    {
+    }
+}

Wino.Core/Services/SynchronizationManager.cs

@@ -370,6 +370,26 @@ public class SynchronizationManager : ISynchronizationManager, IRecipient<Accoun
         return await SynchronizeMailAsync(options, cancellationToken);
     }
 
+    /// <summary>
+    /// Handles category synchronization for the given account.
+    /// </summary>
+    /// <param name="accountId">Account ID to synchronize categories for</param>
+    /// <param name="cancellationToken">Cancellation token</param>
+    /// <returns>Synchronization result</returns>
+    public async Task<MailSynchronizationResult> SynchronizeCategoriesAsync(Guid accountId,
+                                                                            CancellationToken cancellationToken = default)
+    {
+        EnsureInitialized();
+
+        var options = new MailSynchronizationOptions
+        {
+            AccountId = accountId,
+            Type = MailSynchronizationType.Categories
+        };
+
+        return await SynchronizeMailAsync(options, cancellationToken);
+    }
+
     /// <summary>
     /// Handles profile synchronization for the given account.
     /// </summary>

Wino.Core/Services/SynchronizerFactory.cs

@@ -26,6 +26,7 @@ public class SynchronizerFactory : ISynchronizerFactory
     private readonly ICalDavClient _calDavClient;
     private readonly IAutoDiscoveryService _autoDiscoveryService;
     private readonly ICalendarService _calendarService;
+    private readonly IMailCategoryService _mailCategoryService;
 
     private readonly List<IWinoSynchronizerBase> synchronizerCache = new();
 
@@ -41,7 +42,8 @@ public class SynchronizerFactory : ISynchronizerFactory
                                UnifiedImapSynchronizer unifiedImapSynchronizer,
                                ICalDavClient calDavClient,
                                IAutoDiscoveryService autoDiscoveryService,
-                               ICalendarService calendarService)
+                               ICalendarService calendarService,
+                               IMailCategoryService mailCategoryService)
     {
         _outlookChangeProcessor = outlookChangeProcessor;
         _gmailChangeProcessor = gmailChangeProcessor;
@@ -56,6 +58,7 @@ public class SynchronizerFactory : ISynchronizerFactory
         _calDavClient = calDavClient;
         _autoDiscoveryService = autoDiscoveryService;
         _calendarService = calendarService;
+        _mailCategoryService = mailCategoryService;
     }
 
     public async Task<IWinoSynchronizerBase> GetAccountSynchronizerAsync(Guid accountId)
@@ -86,7 +89,7 @@ public class SynchronizerFactory : ISynchronizerFactory
         {
             case Domain.Enums.MailProviderType.Outlook:
                 var outlookAuthenticator = _authenticationProvider.GetAuthenticator(Domain.Enums.MailProviderType.Outlook) as IOutlookAuthenticator;
-                return new OutlookSynchronizer(mailAccount, outlookAuthenticator, _outlookChangeProcessor, _outlookSynchronizerErrorHandlerFactory);
+                return new OutlookSynchronizer(mailAccount, outlookAuthenticator, _outlookChangeProcessor, _outlookSynchronizerErrorHandlerFactory, _mailCategoryService);
             case Domain.Enums.MailProviderType.Gmail:
                 var gmailAuthenticator = _authenticationProvider.GetAuthenticator(Domain.Enums.MailProviderType.Gmail) as IGmailAuthenticator;
                 return new GmailSynchronizer(mailAccount, gmailAuthenticator, _gmailChangeProcessor, _gmailSynchronizerErrorHandlerFactory);

Wino.Core/Services/WinoRequestDelegator.cs

@@ -207,6 +207,21 @@ public class WinoRequestDelegator : IWinoRequestDelegator
         await QueueCalendarSynchronizationAsync(accountId);
     }
 
+    public async Task ExecuteAsync(Guid accountId, IEnumerable<IRequestBase> requests)
+    {
+        var requestList = requests?.Where(a => a != null).ToList() ?? [];
+        if (requestList.Count == 0)
+            return;
+
+        foreach (var request in requestList)
+        {
+            await QueueRequestAsync(request, accountId).ConfigureAwait(false);
+        }
+
+        await SendSyncActionsAddedAsync(requestList, accountId).ConfigureAwait(false);
+        await QueueSynchronizationAsync(accountId).ConfigureAwait(false);
+    }
+
     private async Task<IRequestBase> CreateCalendarEventRequestAsync(CalendarOperationPreparationRequest calendarPreparationRequest)
     {
         var composeResult = calendarPreparationRequest.ComposeResult

Wino.Core/Synchronizers/OutlookSynchronizer.cs

@@ -41,6 +41,7 @@ using Wino.Core.Integration.Processors;
 using Wino.Core.Misc;
 using Wino.Core.Requests.Bundles;
 using Wino.Core.Requests.Calendar;
+using Wino.Core.Requests.Category;
 using Wino.Core.Requests.Folder;
 using Wino.Core.Requests.Mail;
 using Wino.Messaging.UI;
@@ -107,6 +108,7 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
         "ParentFolderId",
         "InternetMessageId",
         "InternetMessageHeaders",
+        "Categories",
     ];
 
     private readonly SemaphoreSlim _handleItemRetrievalSemaphore = new(1);
@@ -116,6 +118,7 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
     private readonly IOutlookChangeProcessor _outlookChangeProcessor;
     private readonly GraphServiceClient _graphClient;
     private readonly IOutlookSynchronizerErrorHandlerFactory _errorHandlingFactory;
+    private readonly IMailCategoryService _mailCategoryService;
     private bool _isFolderStructureChanged;
 
     private readonly SemaphoreSlim _concurrentDownloadSemaphore = new(10); // Limit to 10 concurrent downloads
@@ -123,7 +126,8 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
     public OutlookSynchronizer(MailAccount account,
                                IAuthenticator authenticator,
                                IOutlookChangeProcessor outlookChangeProcessor,
-                               IOutlookSynchronizerErrorHandlerFactory errorHandlingFactory) : base(account, WeakReferenceMessenger.Default)
+                               IOutlookSynchronizerErrorHandlerFactory errorHandlingFactory,
+                               IMailCategoryService mailCategoryService) : base(account, WeakReferenceMessenger.Default)
     {
         var tokenProvider = new MicrosoftTokenProvider(Account, authenticator);
 
@@ -138,6 +142,7 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
 
         _outlookChangeProcessor = outlookChangeProcessor;
         _errorHandlingFactory = errorHandlingFactory;
+        _mailCategoryService = mailCategoryService;
     }
 
     #region MS Graph Handlers
@@ -1152,6 +1157,11 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
                     _logger.Debug("Updating flag status for mail {MessageId}: IsFlagged={IsFlagged}", item.Id, isFlagged);
                     await _outlookChangeProcessor.ChangeFlagStatusAsync(item.Id, isFlagged).ConfigureAwait(false);
                 }
+
+                if (item.Categories != null)
+                {
+                    await ReplaceMailAssignmentsAsync(item.Id, item.Categories).ConfigureAwait(false);
+                }
             }
             else
             {
@@ -1208,6 +1218,43 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
         }
     }
 
+    protected override async Task SynchronizeCategoriesAsync(CancellationToken cancellationToken = default)
+    {
+        var response = await _graphClient.Me.Outlook.MasterCategories
+            .GetAsync(cancellationToken: cancellationToken)
+            .ConfigureAwait(false);
+
+        var categories = response?.Value?
+            .Where(a => !string.IsNullOrWhiteSpace(a?.DisplayName))
+            .Select(a =>
+            {
+                var colorOption = GetMailCategoryColorOption(a.Color);
+
+                return new MailCategory
+                {
+                    MailAccountId = Account.Id,
+                    RemoteId = a.Id,
+                    Name = a.DisplayName,
+                    BackgroundColorHex = colorOption.BackgroundColorHex,
+                    TextColorHex = colorOption.TextColorHex,
+                    Source = MailCategorySource.Outlook
+                };
+            })
+            .ToList() ?? [];
+
+        await _mailCategoryService.ReplaceCategoriesAsync(Account.Id, categories).ConfigureAwait(false);
+    }
+
+    private async Task ReplaceMailAssignmentsAsync(string messageId, IEnumerable<string> categoryNames)
+    {
+        var localMailCopies = await _outlookChangeProcessor.GetMailCopiesAsync([messageId]).ConfigureAwait(false);
+
+        foreach (var localMailCopy in localMailCopies)
+        {
+            await _mailCategoryService.ReplaceMailAssignmentsAsync(Account.Id, localMailCopy.UniqueId, categoryNames ?? []).ConfigureAwait(false);
+        }
+    }
+
     private async Task<OutlookSpecialFolderIdInformation> GetSpecialFolderIdsAsync(CancellationToken cancellationToken)
     {
         var localFolders = await _outlookChangeProcessor.GetLocalFoldersAsync(Account.Id).ConfigureAwait(false);
@@ -1767,6 +1814,87 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
         return Move(batchMoveRequest);
     }
 
+    public override List<IRequestBundle<RequestInformation>> UpdateCategories(BatchMailCategoryAssignmentRequest request)
+        => ForEachRequest(request, item => CreateMessageCategoryPatchRequest(item.Item.Id, item.CategoryNames));
+
+    public override List<IRequestBundle<RequestInformation>> CreateCategory(MailCategoryCreateRequest request)
+    {
+        var outlookCategory = new OutlookCategory
+        {
+            DisplayName = request.Category.Name,
+            Color = GetOutlookCategoryColor(request.Category)
+        };
+
+        var requestInfo = _graphClient.Me.Outlook.MasterCategories.ToPostRequestInformation(outlookCategory);
+        return [new HttpRequestBundle<RequestInformation>(requestInfo, request)];
+    }
+
+    public override List<IRequestBundle<RequestInformation>> UpdateCategory(MailCategoryUpdateRequest request)
+    {
+        if (string.IsNullOrWhiteSpace(request.PreviousRemoteId))
+            return CreateCategory(new MailCategoryCreateRequest(request.Category));
+
+        var hasNameChanged = !string.Equals(request.PreviousName, request.Category.Name, StringComparison.Ordinal);
+        if (!hasNameChanged)
+        {
+            var requestInfo = _graphClient.Me.Outlook.MasterCategories[request.PreviousRemoteId].ToPatchRequestInformation(new OutlookCategory
+            {
+                Color = GetOutlookCategoryColor(request.Category)
+            });
+
+            return [new HttpRequestBundle<RequestInformation>(requestInfo, request)];
+        }
+
+        var bundles = new List<IRequestBundle<RequestInformation>>();
+        var createRequestInfo = _graphClient.Me.Outlook.MasterCategories.ToPostRequestInformation(new OutlookCategory
+        {
+            DisplayName = request.Category.Name,
+            Color = GetOutlookCategoryColor(request.Category)
+        });
+
+        bundles.Add(new HttpRequestBundle<RequestInformation>(createRequestInfo, request));
+
+        foreach (var target in request.AffectedMessages ?? [])
+        {
+            bundles.Add(new HttpRequestBundle<RequestInformation>(
+                CreateMessageCategoryPatchRequest(target.MessageId, target.CategoryNames),
+                request));
+        }
+
+        bundles.Add(new HttpRequestBundle<RequestInformation>(
+            _graphClient.Me.Outlook.MasterCategories[request.PreviousRemoteId].ToDeleteRequestInformation(),
+            request));
+
+        return bundles;
+    }
+
+    public override List<IRequestBundle<RequestInformation>> DeleteCategory(MailCategoryDeleteRequest request)
+    {
+        if (string.IsNullOrWhiteSpace(request.PreviousRemoteId))
+            return [];
+
+        var bundles = new List<IRequestBundle<RequestInformation>>();
+
+        foreach (var target in request.AffectedMessages ?? [])
+        {
+            bundles.Add(new HttpRequestBundle<RequestInformation>(
+                CreateMessageCategoryPatchRequest(target.MessageId, target.CategoryNames),
+                request));
+        }
+
+        bundles.Add(new HttpRequestBundle<RequestInformation>(
+            _graphClient.Me.Outlook.MasterCategories[request.PreviousRemoteId].ToDeleteRequestInformation(),
+            request));
+
+        return bundles;
+    }
+
+    private RequestInformation CreateMessageCategoryPatchRequest(string messageId, IReadOnlyList<string> categoryNames)
+        => _graphClient.Me.Messages[messageId].ToPatchRequestInformation(new Message
+        {
+            Categories = categoryNames?.ToList() ?? []
+        });
+
     public override async Task DownloadMissingMimeMessageAsync(MailCopy mailItem,
                                                            MailKit.ITransferProgress transferProgress = null,
                                                            CancellationToken cancellationToken = default)
@@ -1962,7 +2090,9 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
         for (int i = 0; i < itemCount; i++)
         {
             var bundle = batch.ElementAt(i);
-            requiresSerial |= bundle.UIChangeRequest is SendDraftRequest;
+            requiresSerial |= bundle.UIChangeRequest is SendDraftRequest
+                              or MailCategoryUpdateRequest
+                              or MailCategoryDeleteRequest;
 
             // UI changes are already applied in ExecuteNativeRequestsAsync before batching.
             var batchRequestId = await batchContent.AddBatchRequestStepAsync(bundle.NativeRequest);
@@ -2110,7 +2240,10 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
            || request is ChangeFlagRequest
            || request is MarkReadRequest
            || request is ArchiveRequest
+           || request is MailCategoryAssignmentRequest
            || request is RenameFolderRequest
+           || request is MailCategoryUpdateRequest
+           || request is MailCategoryDeleteRequest
            || request is DeleteFolderRequest
            || request is AcceptEventRequest
            || request is DeclineEventRequest
@@ -2165,6 +2298,26 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
                     return;
 
                 await UploadCalendarEventAttachmentsAsync(createCalendarEventRequest, createdEventId, CancellationToken.None).ConfigureAwait(false);
+                return;
+            }
+
+            if (bundle?.UIChangeRequest is MailCategoryCreateRequest createCategoryRequest)
+            {
+                var createdCategoryId = json?["id"]?.GetValue<string>();
+                if (!string.IsNullOrWhiteSpace(createdCategoryId))
+                {
+                    await _mailCategoryService.UpdateRemoteIdAsync(createCategoryRequest.Category.Id, createdCategoryId).ConfigureAwait(false);
+                }
+                return;
+            }
+
+            if (bundle?.UIChangeRequest is MailCategoryUpdateRequest updateCategoryRequest)
+            {
+                var updatedCategoryId = json?["id"]?.GetValue<string>();
+                if (!string.IsNullOrWhiteSpace(updatedCategoryId))
+                {
+                    await _mailCategoryService.UpdateRemoteIdAsync(updateCategoryRequest.Category.Id, updatedCategoryId).ConfigureAwait(false);
+                }
             }
         }
         catch (Exception ex)
@@ -2367,11 +2520,68 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
         // Outlook messages can only be assigned to 1 folder at a time.
         // Therefore we don't need to create multiple copies of the same message for different folders.
         var contacts = ExtractContactsFromOutlookMessage(message);
-        var package = new NewMailItemPackage(mailCopy, mimeMessage, assignedFolder.RemoteFolderId, contacts);
+        var package = new NewMailItemPackage(mailCopy, mimeMessage, assignedFolder.RemoteFolderId, contacts, message.Categories);
 
         return [package];
     }
 
+    private static MailCategoryColorOption GetMailCategoryColorOption(CategoryColor? color)
+        => color switch
+        {
+            CategoryColor.Preset0 => new("#FEE2E2", "#991B1B"),
+            CategoryColor.Preset1 => new("#FFEDD5", "#9A3412"),
+            CategoryColor.Preset2 => new("#FEF3C7", "#92400E"),
+            CategoryColor.Preset3 => new("#ECFCCB", "#3F6212"),
+            CategoryColor.Preset4 => new("#DCFCE7", "#166534"),
+            CategoryColor.Preset5 => new("#CCFBF1", "#115E59"),
+            CategoryColor.Preset6 => new("#CFFAFE", "#155E75"),
+            CategoryColor.Preset7 => new("#DBEAFE", "#1D4ED8"),
+            CategoryColor.Preset8 => new("#E0E7FF", "#4338CA"),
+            CategoryColor.Preset9 => new("#F3E8FF", "#7E22CE"),
+            CategoryColor.Preset10 => new("#FCE7F3", "#9D174D"),
+            CategoryColor.Preset11 => new("#FECACA", "#7F1D1D"),
+            CategoryColor.Preset12 => new("#FED7AA", "#7C2D12"),
+            CategoryColor.Preset13 => new("#FDE68A", "#78350F"),
+            CategoryColor.Preset14 => new("#D9F99D", "#365314"),
+            CategoryColor.Preset15 => new("#BBF7D0", "#14532D"),
+            CategoryColor.Preset16 => new("#99F6E4", "#134E4A"),
+            CategoryColor.Preset17 => new("#A5F3FC", "#164E63"),
+            CategoryColor.Preset18 => new("#BFDBFE", "#1E3A8A"),
+            CategoryColor.Preset19 => new("#DDD6FE", "#5B21B6"),
+            CategoryColor.Preset20 => new("#E5E7EB", "#374151"),
+            CategoryColor.Preset21 => new("#D1D5DB", "#1F2937"),
+            CategoryColor.Preset22 => new("#F3F4F6", "#111827"),
+            CategoryColor.Preset23 => new("#E2E8F0", "#334155"),
+            CategoryColor.Preset24 => new("#F8FAFC", "#475569"),
+            _ => new("#E5E7EB", "#374151")
+        };
+
+    private static CategoryColor GetOutlookCategoryColor(MailCategory category)
+        => (category.BackgroundColorHex?.ToUpperInvariant(), category.TextColorHex?.ToUpperInvariant()) switch
+        {
+            ("#FEE2E2", "#991B1B") => CategoryColor.Preset0,
+            ("#FFEDD5", "#9A3412") => CategoryColor.Preset1,
+            ("#FEF3C7", "#92400E") => CategoryColor.Preset2,
+            ("#ECFCCB", "#3F6212") => CategoryColor.Preset3,
+            ("#DCFCE7", "#166534") => CategoryColor.Preset4,
+            ("#CCFBF1", "#115E59") => CategoryColor.Preset5,
+            ("#CFFAFE", "#155E75") => CategoryColor.Preset6,
+            ("#DBEAFE", "#1D4ED8") => CategoryColor.Preset7,
+            ("#E0E7FF", "#4338CA") => CategoryColor.Preset8,
+            ("#F3E8FF", "#7E22CE") => CategoryColor.Preset9,
+            ("#FCE7F3", "#9D174D") => CategoryColor.Preset10,
+            ("#FECACA", "#7F1D1D") => CategoryColor.Preset11,
+            ("#FED7AA", "#7C2D12") => CategoryColor.Preset12,
+            ("#FDE68A", "#78350F") => CategoryColor.Preset13,
+            ("#D9F99D", "#365314") => CategoryColor.Preset14,
+            ("#BBF7D0", "#14532D") => CategoryColor.Preset15,
+            ("#99F6E4", "#134E4A") => CategoryColor.Preset16,
+            ("#A5F3FC", "#164E63") => CategoryColor.Preset17,
+            ("#BFDBFE", "#1E3A8A") => CategoryColor.Preset18,
+            ("#DDD6FE", "#5B21B6") => CategoryColor.Preset19,
+            _ => CategoryColor.Preset0
+        };
+
     private async Task TryMapCalendarInvitationAsync(MailCopy mailCopy, MimeMessage mimeMessage, CancellationToken cancellationToken)
     {
         if (mailCopy.ItemType != MailItemType.CalendarInvitation || mimeMessage == null)

Wino.Core/Synchronizers/WinoSynchronizer.cs

@@ -20,6 +20,7 @@ using Wino.Core.Domain.Models.MailItem;
 using Wino.Core.Domain.Models.Synchronization;
 using Wino.Core.Requests.Bundles;
 using Wino.Core.Requests.Calendar;
+using Wino.Core.Requests.Category;
 using Wino.Core.Requests.Folder;
 using Wino.Core.Requests.Mail;
 using Wino.Messaging.UI;
@@ -63,6 +64,7 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
     /// Only available for Gmail right now.
     /// </summary>
     protected virtual Task SynchronizeAliasesAsync() => Task.CompletedTask;
+    protected virtual Task SynchronizeCategoriesAsync(CancellationToken cancellationToken = default) => Task.CompletedTask;
 
     /// <summary>
     /// Queues all mail ids for initial synchronization for a specific folder.
@@ -194,6 +196,9 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
                             case MailSynchronizerOperation.Archive:
                                 nativeRequests.AddRange(Archive(new BatchArchiveRequest(group.Cast<ArchiveRequest>())));
                                 break;
+                            case MailSynchronizerOperation.UpdateCategories:
+                                nativeRequests.AddRange(UpdateCategories(new BatchMailCategoryAssignmentRequest(group.Cast<MailCategoryAssignmentRequest>())));
+                                break;
                             default:
                                 break;
                         }
@@ -221,6 +226,23 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
                                 break;
                         }
                     }
+                    else if (key is CategorySynchronizerOperation categorySynchronizerOperation)
+                    {
+                        switch (categorySynchronizerOperation)
+                        {
+                            case CategorySynchronizerOperation.CreateCategory:
+                                nativeRequests.AddRange(CreateCategory(group.ElementAt(0) as MailCategoryCreateRequest));
+                                break;
+                            case CategorySynchronizerOperation.UpdateCategory:
+                                nativeRequests.AddRange(UpdateCategory(group.ElementAt(0) as MailCategoryUpdateRequest));
+                                break;
+                            case CategorySynchronizerOperation.DeleteCategory:
+                                nativeRequests.AddRange(DeleteCategory(group.ElementAt(0) as MailCategoryDeleteRequest));
+                                break;
+                            default:
+                                break;
+                        }
+                    }
                 }
 
                 changeRequestQueue.Clear();
@@ -322,6 +344,30 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
                 }
             }
 
+            // Category definition sync.
+            if (options.Type == MailSynchronizationType.Categories)
+            {
+                if (!Account.IsCategorySyncSupported) return MailSynchronizationResult.Empty;
+
+                try
+                {
+                    await SynchronizeCategoriesAsync(activeSynchronizationCancellationToken);
+
+                    return FinalizeMailResult(MailSynchronizationResult.Empty);
+                }
+                catch (AuthenticationAttentionException)
+                {
+                    throw;
+                }
+                catch (Exception ex)
+                {
+                    Log.Error(ex, "Failed to update categories for {Name}", Account.Name);
+
+                    CaptureSynchronizationIssue(SynchronizationIssue.FromException(ex, "CategorySync"));
+                    return FinalizeMailResult(MailSynchronizationResult.Failed(ex));
+                }
+            }
+
             if (shouldDelayExecution)
             {
                 await Task.Delay(maxExecutionDelay);
@@ -526,6 +572,16 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
     /// <returns>New synchronization options with minimal HTTP effort.</returns>
     private MailSynchronizationOptions GetSynchronizationOptionsAfterRequestExecution(List<IRequestBase> requests, Guid existingSynchronizationId)
     {
+        if (requests.All(a => a is ICategoryActionRequest or MailCategoryAssignmentRequest))
+        {
+            return new MailSynchronizationOptions
+            {
+                AccountId = Account.Id,
+                Id = existingSynchronizationId,
+                Type = MailSynchronizationType.FoldersOnly
+            };
+        }
+
         List<Guid> synchronizationFolderIds = requests
                 .Where(a => a is ICustomFolderSynchronizationRequest)
                 .Cast<ICustomFolderSynchronizationRequest>()
@@ -602,6 +658,10 @@ public abstract class WinoSynchronizer<TBaseRequest, TMessageType, TCalendarEven
     public virtual List<IRequestBundle<TBaseRequest>> MarkFolderAsRead(MarkFolderAsReadRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
     public virtual List<IRequestBundle<TBaseRequest>> DeleteFolder(DeleteFolderRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
     public virtual List<IRequestBundle<TBaseRequest>> CreateSubFolder(CreateSubFolderRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
+    public virtual List<IRequestBundle<TBaseRequest>> UpdateCategories(BatchMailCategoryAssignmentRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
+    public virtual List<IRequestBundle<TBaseRequest>> CreateCategory(MailCategoryCreateRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
+    public virtual List<IRequestBundle<TBaseRequest>> UpdateCategory(MailCategoryUpdateRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
+    public virtual List<IRequestBundle<TBaseRequest>> DeleteCategory(MailCategoryDeleteRequest request) => throw new NotSupportedException(string.Format(Translator.Exception_UnsupportedSynchronizerOperation, this.GetType()));
 
     #endregion
 

Wino.Mail.ViewModels/AccountDetailsPageViewModel.cs

@@ -169,6 +169,10 @@ public partial class AccountDetailsPageViewModel : MailBaseViewModel
     private void EditAliases()
         => Messenger.Send(new BreadcrumbNavigationRequested(Translator.SettingsManageAliases_Title, WinoPage.AliasManagementPage, Account.Id));
 
+    [RelayCommand]
+    private void EditCategories()
+        => Messenger.Send(new BreadcrumbNavigationRequested(Translator.MailCategoryManagementPage_Title, WinoPage.MailCategoryManagementPage, Account.Id));
+
     [RelayCommand]
     private void EditImapCalDavSettings()
         => Messenger.Send(new BreadcrumbNavigationRequested(

Wino.Mail.ViewModels/AccountSetupProgressPageViewModel.cs

@@ -81,6 +81,10 @@ public partial class AccountSetupProgressPageViewModel : MailBaseViewModel
             Steps.Add(new AccountSetupStepModel { Title = Translator.AccountSetup_Step_FetchingProfile });
             Steps.Add(new AccountSetupStepModel { Title = Translator.AccountSetup_Step_SavingAccount });
             Steps.Add(new AccountSetupStepModel { Title = Translator.AccountSetup_Step_SyncingFolders });
+            if (WizardContext.SelectedProvider.Type == MailProviderType.Outlook)
+            {
+                Steps.Add(new AccountSetupStepModel { Title = Translator.AccountSetup_Step_SyncingCategories });
+            }
             Steps.Add(new AccountSetupStepModel { Title = Translator.AccountSetup_Step_FetchingCalendarMetadata });
             Steps.Add(new AccountSetupStepModel { Title = Translator.AccountSetup_Step_SyncingAliases });
             Steps.Add(new AccountSetupStepModel { Title = Translator.AccountSetup_Step_Finalizing });
@@ -229,6 +233,16 @@ public partial class AccountSetupProgressPageViewModel : MailBaseViewModel
                     throw new Exception(Translator.Exception_FailedToSynchronizeFolders);
                 SetCurrentStepSucceeded();
 
+                // Step: Categories
+                if (_createdAccount.IsCategorySyncSupported)
+                {
+                    SetStepInProgress(Translator.AccountSetup_Step_SyncingCategories);
+                    var categoryResult = await SynchronizationManager.Instance.SynchronizeCategoriesAsync(_createdAccount.Id);
+                    if (categoryResult.CompletedState != SynchronizationCompletedState.Success)
+                        throw new Exception(Translator.Exception_FailedToSynchronizeCategories);
+                    SetCurrentStepSucceeded();
+                }
+
                 // Step: Calendar metadata
                 SetStepInProgress(Translator.AccountSetup_Step_FetchingCalendarMetadata);
                 if (_createdAccount.IsCalendarAccessGranted)

Wino.Mail.ViewModels/MailAppShellViewModel.cs

@@ -73,6 +73,7 @@ public partial class MailAppShellViewModel : MailBaseViewModel,
     public IMenuItem CreatePrimaryMenuItem => CreateMailMenuItem;
 
     private readonly IFolderService _folderService;
+    private readonly IMailCategoryService _mailCategoryService;
     private readonly IConfigurationService _configurationService;
     private readonly IStartupBehaviorService _startupBehaviorService;
     private readonly IAccountService _accountService;
@@ -99,6 +100,7 @@ public partial class MailAppShellViewModel : MailBaseViewModel,
                              IMimeFileService mimeFileService,
                              INativeAppService nativeAppService,
                              IMailService mailService,
+                             IMailCategoryService mailCategoryService,
                              IAccountService accountService,
                              IContextMenuItemService contextMenuItemService,
                              IStoreRatingService storeRatingService,
@@ -125,6 +127,7 @@ public partial class MailAppShellViewModel : MailBaseViewModel,
         _mimeFileService = mimeFileService;
         _nativeAppService = nativeAppService;
         _mailService = mailService;
+        _mailCategoryService = mailCategoryService;
         _folderService = folderService;
         _accountService = accountService;
         _contextMenuItemService = contextMenuItemService;
@@ -721,7 +724,8 @@ public partial class MailAppShellViewModel : MailBaseViewModel,
         {
             await HandleCreateNewMailAsync();
         }
-        else if (clickedMenuItem is IBaseFolderMenuItem baseFolderMenuItem && baseFolderMenuItem.HandlingFolders.All(a => a.IsMoveTarget))
+        else if (clickedMenuItem is IBaseFolderMenuItem baseFolderMenuItem &&
+                 (clickedMenuItem is IMailCategoryMenuItem or IMergedMailCategoryMenuItem || baseFolderMenuItem.HandlingFolders.All(a => a.IsMoveTarget)))
         {
             // Don't navigate to base folders that contain non-move target folders.
             // Theory: This is a special folder like Categories or More. Don't navigate to it.
@@ -793,11 +797,20 @@ public partial class MailAppShellViewModel : MailBaseViewModel,
     {
         // Get visible account menu items, ordered by merged accounts at the last.
         // We will update the unread counts for all single accounts and trigger UI refresh for merged menu items.
-        var accountMenuItems = MenuItems.GetAllAccountMenuItems().OrderBy(a => a.HoldingAccounts.Count());
+        List<IAccountMenuItem> accountMenuItems = null;
+
+        await ExecuteUIThread(() =>
+        {
+            accountMenuItems = MenuItems
+                .GetAllAccountMenuItems()
+                .OrderBy(a => a.HoldingAccounts.Count())
+                .ToList();
+        });
 
         // Individually get all single accounts' unread counts.
-        var accountIds = accountMenuItems.OfType<AccountMenuItem>().Select(a => a.AccountId);
+        var accountIds = accountMenuItems.OfType<AccountMenuItem>().Select(a => a.AccountId).ToList();
         var unreadCountResult = await _folderService.GetUnreadItemCountResultsAsync(accountIds).ConfigureAwait(false);
+        var unreadCategoryCountResult = await _mailCategoryService.GetUnreadCategoryCountResultsAsync(accountIds).ConfigureAwait(false);
 
         // Recursively update all folders' unread counts to 0.
         // Query above only returns unread counts that exists. We need to reset the rest to 0 first.
@@ -849,6 +862,29 @@ public partial class MailAppShellViewModel : MailBaseViewModel,
             }
         }
 
+        foreach (var unreadCategoryCount in unreadCategoryCountResult)
+        {
+            if (MenuItems.TryGetCategoryMenuItem(unreadCategoryCount.CategoryId, out var categoryMenuItem))
+            {
+                if (categoryMenuItem is IMergedMailCategoryMenuItem mergedCategoryMenuItem)
+                {
+                    await ExecuteUIThread(() =>
+                    {
+                        categoryMenuItem.UnreadItemCount = unreadCategoryCountResult
+                            .Where(a => mergedCategoryMenuItem.Categories.Any(b => b.Id == a.CategoryId))
+                            .Sum(a => a.UnreadItemCount);
+                    });
+                }
+                else
+                {
+                    await ExecuteUIThread(() =>
+                    {
+                        categoryMenuItem.UnreadItemCount = unreadCategoryCount.UnreadItemCount;
+                    });
+                }
+            }
+        }
+
         // Update unread badge after all unread counts are updated.
         await _notificationBuilder.UpdateTaskbarIconBadgeAsync();
     }

Wino.Mail.ViewModels/MailCategoryManagementPageViewModel.cs

@@ -0,0 +1,251 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Linq;
+using System.Threading.Tasks;
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Wino.Core.Domain;
+using Wino.Core.Domain.Entities.Mail;
+using Wino.Core.Domain.Entities.Shared;
+using Wino.Core.Domain.Enums;
+using Wino.Core.Domain.Interfaces;
+using Wino.Core.Domain.Models.MailItem;
+using Wino.Core.Domain.Models.Navigation;
+using Wino.Core.Domain.Models.Synchronization;
+using Wino.Core.Requests.Category;
+using Wino.Core.Services;
+
+namespace Wino.Mail.ViewModels;
+
+public partial class MailCategoryManagementPageViewModel : MailBaseViewModel
+{
+    private readonly IMailCategoryService _mailCategoryService;
+    private readonly IAccountService _accountService;
+    private readonly IMailDialogService _dialogService;
+    private readonly IWinoRequestDelegator _winoRequestDelegator;
+
+    [ObservableProperty]
+    [NotifyPropertyChangedFor(nameof(CanRefresh))]
+    public partial MailAccount Account { get; set; }
+
+    public ObservableCollection<MailCategory> Categories { get; } = [];
+
+    public bool CanRefresh => Account?.ProviderType == MailProviderType.Outlook;
+    public bool HasCategories => Categories.Count > 0;
+
+    public MailCategoryManagementPageViewModel(
+        IMailCategoryService mailCategoryService,
+        IAccountService accountService,
+        IMailDialogService dialogService,
+        IWinoRequestDelegator winoRequestDelegator)
+    {
+        _mailCategoryService = mailCategoryService;
+        _accountService = accountService;
+        _dialogService = dialogService;
+        _winoRequestDelegator = winoRequestDelegator;
+    }
+
+    public override async void OnNavigatedTo(NavigationMode mode, object parameters)
+    {
+        base.OnNavigatedTo(mode, parameters);
+
+        if (parameters is not Guid accountId)
+            return;
+
+        Account = await _accountService.GetAccountAsync(accountId).ConfigureAwait(false);
+
+        if (Account != null)
+        {
+            await LoadCategoriesAsync().ConfigureAwait(false);
+        }
+    }
+
+    [RelayCommand]
+    private Task AddCategoryAsync()
+        => CreateOrUpdateCategoryAsync();
+
+    [RelayCommand]
+    private async Task RefreshCategoriesAsync()
+    {
+        if (!CanRefresh)
+            return;
+
+        var shouldContinue = await _dialogService.ShowConfirmationDialogAsync(
+            Translator.MailCategoryManagementPage_RefreshConfirmationMessage,
+            Translator.Buttons_Refresh,
+            Translator.Buttons_Refresh).ConfigureAwait(false);
+
+        if (!shouldContinue)
+            return;
+
+        await _mailCategoryService.DeleteCategoriesAsync(Account.Id).ConfigureAwait(false);
+        await SynchronizationManager.Instance.SynchronizeCategoriesAsync(Account.Id).ConfigureAwait(false);
+
+        await LoadCategoriesAsync().ConfigureAwait(false);
+    }
+
+    public Task EditCategoryAsync(MailCategory category)
+        => CreateOrUpdateCategoryAsync(category);
+
+    public async Task DeleteCategoryAsync(MailCategory category)
+    {
+        if (category == null)
+            return;
+
+        var shouldDelete = await _dialogService.ShowConfirmationDialogAsync(
+            string.Format(Translator.MailCategoryManagementPage_DeleteConfirmationMessage, category.Name),
+            Translator.MailCategoryManagementPage_DeleteConfirmationTitle,
+            Translator.Buttons_Delete).ConfigureAwait(false);
+
+        if (!shouldDelete)
+            return;
+
+        var deleteRequest = await BuildDeleteCategoryRequestAsync(category).ConfigureAwait(false);
+        await _mailCategoryService.DeleteCategoryAsync(category.Id).ConfigureAwait(false);
+        await QueueOutlookCategoryRequestsAsync(deleteRequest).ConfigureAwait(false);
+        await LoadCategoriesAsync().ConfigureAwait(false);
+    }
+
+    public async Task SetFavoriteAsync(MailCategory category, bool isFavorite)
+    {
+        if (category == null)
+            return;
+
+        await _mailCategoryService.ToggleFavoriteAsync(category.Id, isFavorite).ConfigureAwait(false);
+        await LoadCategoriesAsync().ConfigureAwait(false);
+    }
+
+    private async Task CreateOrUpdateCategoryAsync(MailCategory existingCategory = null)
+    {
+        var dialogResult = await _dialogService.ShowEditMailCategoryDialogAsync(existingCategory).ConfigureAwait(false);
+        if (dialogResult == null)
+            return;
+
+        if (string.IsNullOrWhiteSpace(dialogResult.Name))
+        {
+            await _dialogService.ShowMessageAsync(
+                Translator.MailCategoryDialog_InvalidNameMessage,
+                Translator.MailCategoryDialog_InvalidNameTitle,
+                WinoCustomMessageDialogIcon.Warning).ConfigureAwait(false);
+            return;
+        }
+
+        var normalizedName = dialogResult.Name.Trim();
+        var categoryIdToExclude = existingCategory?.Id;
+        var alreadyExists = await _mailCategoryService.CategoryNameExistsAsync(Account.Id, normalizedName, categoryIdToExclude).ConfigureAwait(false);
+
+        if (alreadyExists)
+        {
+            await _dialogService.ShowMessageAsync(
+                Translator.MailCategoryDialog_DuplicateMessage,
+                Translator.MailCategoryDialog_DuplicateTitle,
+                WinoCustomMessageDialogIcon.Warning).ConfigureAwait(false);
+            return;
+        }
+
+        if (existingCategory == null)
+        {
+            var newCategory = new MailCategory
+            {
+                Id = Guid.NewGuid(),
+                MailAccountId = Account.Id,
+                Name = normalizedName,
+                BackgroundColorHex = dialogResult.BackgroundColorHex,
+                TextColorHex = dialogResult.TextColorHex,
+                Source = Account.ProviderType == MailProviderType.Outlook ? MailCategorySource.Outlook : MailCategorySource.Local
+            };
+
+            await _mailCategoryService.CreateCategoryAsync(newCategory).ConfigureAwait(false);
+
+            if (Account.ProviderType == MailProviderType.Outlook)
+            {
+                await _winoRequestDelegator.ExecuteAsync(Account.Id, [new MailCategoryCreateRequest(newCategory)]).ConfigureAwait(false);
+            }
+        }
+        else
+        {
+            var previousName = existingCategory.Name;
+            var previousRemoteId = existingCategory.RemoteId;
+
+            existingCategory.Name = normalizedName;
+            existingCategory.BackgroundColorHex = dialogResult.BackgroundColorHex;
+            existingCategory.TextColorHex = dialogResult.TextColorHex;
+
+            await _mailCategoryService.UpdateCategoryAsync(existingCategory).ConfigureAwait(false);
+
+            if (Account.ProviderType == MailProviderType.Outlook)
+            {
+                if (string.IsNullOrWhiteSpace(previousRemoteId))
+                {
+                    await _winoRequestDelegator.ExecuteAsync(Account.Id, [new MailCategoryCreateRequest(existingCategory)]).ConfigureAwait(false);
+                }
+                else
+                {
+                    var affectedMessages = await BuildAffectedMessageTargetsAsync(existingCategory.Id).ConfigureAwait(false);
+                    var updateRequest = new MailCategoryUpdateRequest(existingCategory, previousName, previousRemoteId, affectedMessages);
+                    await _winoRequestDelegator.ExecuteAsync(Account.Id, [updateRequest]).ConfigureAwait(false);
+                }
+            }
+        }
+
+        await LoadCategoriesAsync().ConfigureAwait(false);
+    }
+
+    private async Task<MailCategoryDeleteRequest> BuildDeleteCategoryRequestAsync(MailCategory category)
+    {
+        if (category == null || Account?.ProviderType != MailProviderType.Outlook)
+            return null;
+
+        var mailCopies = await _mailCategoryService.GetMailCopiesForCategoryAsync(category.Id).ConfigureAwait(false);
+        var affectedMessages = new List<MailCategoryMessageUpdateTarget>();
+
+        foreach (var mailCopy in mailCopies.Where(a => !string.IsNullOrWhiteSpace(a.Id)))
+        {
+            var remainingNames = await _mailCategoryService.GetCategoryNamesForMailAsync(mailCopy.UniqueId).ConfigureAwait(false);
+            var categoryNames = remainingNames
+                .Where(a => !string.Equals(a, category.Name, StringComparison.OrdinalIgnoreCase))
+                .ToList();
+
+            affectedMessages.Add(new MailCategoryMessageUpdateTarget(mailCopy.Id, categoryNames));
+        }
+
+        return new MailCategoryDeleteRequest(category, category.RemoteId, affectedMessages);
+    }
+
+    private async Task<IReadOnlyList<MailCategoryMessageUpdateTarget>> BuildAffectedMessageTargetsAsync(Guid categoryId)
+    {
+        var mailCopies = await _mailCategoryService.GetMailCopiesForCategoryAsync(categoryId).ConfigureAwait(false);
+        var affectedMessages = new List<MailCategoryMessageUpdateTarget>();
+
+        foreach (var mailCopy in mailCopies.Where(a => !string.IsNullOrWhiteSpace(a.Id)))
+        {
+            var categoryNames = await _mailCategoryService.GetCategoryNamesForMailAsync(mailCopy.UniqueId).ConfigureAwait(false);
+            affectedMessages.Add(new MailCategoryMessageUpdateTarget(mailCopy.Id, categoryNames));
+        }
+
+        return affectedMessages;
+    }
+
+    private Task QueueOutlookCategoryRequestsAsync(params IRequestBase[] requests)
+        => Account?.ProviderType == MailProviderType.Outlook && requests.Any(a => a != null)
+            ? _winoRequestDelegator.ExecuteAsync(Account.Id, requests.Where(a => a != null))
+            : Task.CompletedTask;
+
+    private async Task LoadCategoriesAsync()
+    {
+        var categories = await _mailCategoryService.GetCategoriesAsync(Account.Id).ConfigureAwait(false);
+
+        await ExecuteUIThread(() =>
+        {
+            Categories.Clear();
+
+            foreach (var category in categories)
+            {
+                Categories.Add(category);
+            }
+
+            OnPropertyChanged(nameof(HasCategories));
+        });
+    }
+}

Wino.Mail.ViewModels/MailListPageViewModel.cs

@@ -24,6 +24,7 @@ using Wino.Core.Domain.Models.Menus;
 using Wino.Core.Domain.Models.Navigation;
 using Wino.Core.Domain.Models.Reader;
 using Wino.Core.Domain.Models.Synchronization;
+using Wino.Core.Requests.Mail;
 using Wino.Core.Services;
 using Wino.Mail.ViewModels.Collections;
 using Wino.Mail.ViewModels.Data;
@@ -77,6 +78,7 @@ public partial class MailListPageViewModel : MailBaseViewModel,
     private readonly INotificationBuilder _notificationBuilder;
     private readonly IFolderService _folderService;
     private readonly IContextMenuItemService _contextMenuItemService;
+    private readonly IMailCategoryService _mailCategoryService;
     private readonly IWinoRequestDelegator _winoRequestDelegator;
     private readonly IKeyPressService _keyPressService;
     private readonly IWinoLogger _winoLogger;
@@ -156,6 +158,8 @@ public partial class MailListPageViewModel : MailBaseViewModel,
     [ObservableProperty]
     [NotifyPropertyChangedFor(nameof(CanSynchronize))]
     [NotifyPropertyChangedFor(nameof(IsFolderSynchronizationEnabled))]
+    [NotifyPropertyChangedFor(nameof(IsCategoryView))]
+    [NotifyPropertyChangedFor(nameof(IsSyncButtonVisible))]
     public partial IBaseFolderMenuItem ActiveFolder { get; set; }
 
     [ObservableProperty]
@@ -172,6 +176,7 @@ public partial class MailListPageViewModel : MailBaseViewModel,
                                  INotificationBuilder notificationBuilder,
                                  IFolderService folderService,
                                  IContextMenuItemService contextMenuItemService,
+                                 IMailCategoryService mailCategoryService,
                                  IWinoRequestDelegator winoRequestDelegator,
                                  IKeyPressService keyPressService,
                                  IPreferencesService preferencesService,
@@ -185,6 +190,7 @@ public partial class MailListPageViewModel : MailBaseViewModel,
         _mimeFileService = mimeFileService;
         _folderService = folderService;
         _contextMenuItemService = contextMenuItemService;
+        _mailCategoryService = mailCategoryService;
         _winoRequestDelegator = winoRequestDelegator;
         _keyPressService = keyPressService;
 
@@ -277,9 +283,11 @@ public partial class MailListPageViewModel : MailBaseViewModel,
         }
     }
 
-    public bool CanSynchronize => !IsAccountSynchronizerInSynchronization && IsFolderSynchronizationEnabled;
+    public bool CanSynchronize => !IsCategoryView && !IsAccountSynchronizerInSynchronization && IsFolderSynchronizationEnabled;
     public bool IsFolderSynchronizationEnabled => ActiveFolder?.IsSynchronizationEnabled ?? false;
     public bool IsArchiveSpecialFolder => ActiveFolder?.SpecialFolderType == SpecialFolderType.Archive;
+    public bool IsCategoryView => ActiveFolder is IMailCategoryMenuItem or IMergedMailCategoryMenuItem;
+    public bool IsSyncButtonVisible => !IsCategoryView;
 
     public string SelectedMessageText => IsDragInProgress
         ? string.Format(Translator.MailsDragging, DraggingItemsCount)
@@ -396,9 +404,12 @@ public partial class MailListPageViewModel : MailBaseViewModel,
         }
         else
         {
+            if (IsCategoryView)
+            {
+                PivotFolders.Add(new FolderPivotViewModel(ActiveFolder.FolderName, null));
+            }
             // Merged folders don't support focused feature.
-
+            else if (ActiveFolder is IMergedAccountFolderMenuItem)
-            if (ActiveFolder is IMergedAccountFolderMenuItem)
             {
                 PivotFolders.Add(new FolderPivotViewModel(ActiveFolder.FolderName, null));
             }
@@ -545,7 +556,7 @@ public partial class MailListPageViewModel : MailBaseViewModel,
     [RelayCommand]
     private async Task EnableFolderSynchronizationAsync()
     {
-        if (ActiveFolder == null) return;
+        if (ActiveFolder == null || IsCategoryView) return;
 
         foreach (var folder in ActiveFolder.HandlingFolders)
         {
@@ -561,13 +572,9 @@ public partial class MailListPageViewModel : MailBaseViewModel,
         Debug.WriteLine("Loading more...");
         await ExecuteUIThread(() => { IsInitializingFolder = true; });
 
-        var initializationOptions = new MailListInitializationOptions(ActiveFolder.HandlingFolders,
+        var initializationOptions = CreateInitializationOptions(
-                                                                      SelectedFilterOption.Type,
+            IsInSearchMode ? SearchQuery : string.Empty,
-                                                                      SelectedSortingOption.Type,
+            MailCollection.MailCopyIdHashSet);
-                                                                      PreferencesService.IsThreadingEnabled,
-                                                                      SelectedFolderPivot.IsFocused,
-                                                                      IsInSearchMode ? SearchQuery : string.Empty,
-                                                                      MailCollection.MailCopyIdHashSet);
 
         var items = await _mailService.FetchMailsAsync(initializationOptions).ConfigureAwait(false);
 
@@ -674,6 +681,60 @@ public partial class MailListPageViewModel : MailBaseViewModel,
     public IEnumerable<MailOperationMenuItem> GetAvailableMailActions(IEnumerable<MailItemViewModel> contextMailItems)
         => _contextMenuItemService.GetMailItemContextMenuActions(contextMailItems.Select(a => a.MailCopy));
 
+    public async Task<(IReadOnlyList<MailCategory> Categories, IReadOnlyCollection<Guid> AssignedCategoryIds)> GetAvailableCategoriesAsync(IEnumerable<MailItemViewModel> targetItems)
+    {
+        var targetList = targetItems?.Where(a => a?.MailCopy?.AssignedAccount != null).ToList() ?? [];
+        if (targetList.Count == 0)
+            return ([], []);
+
+        var accountIds = targetList.Select(a => a.MailCopy.AssignedAccount.Id).Distinct().ToList();
+        if (accountIds.Count != 1)
+            return ([], []);
+
+        var accountId = accountIds[0];
+        var uniqueIds = targetList.Select(a => a.MailCopy.UniqueId).Distinct().ToList();
+
+        var categories = await _mailCategoryService.GetCategoriesAsync(accountId).ConfigureAwait(false);
+        var assignedCategoryIds = await _mailCategoryService.GetAssignedCategoryIdsForAllAsync(uniqueIds).ConfigureAwait(false);
+
+        return (categories, assignedCategoryIds);
+    }
+
+    public async Task ToggleCategoryAssignmentAsync(MailCategory category, IEnumerable<MailItemViewModel> targetItems, bool isAssignedToAll)
+    {
+        var targetList = targetItems?.Where(a => a?.MailCopy?.AssignedAccount != null).ToList() ?? [];
+        if (category == null || targetList.Count == 0)
+            return;
+
+        var accountIds = targetList.Select(a => a.MailCopy.AssignedAccount.Id).Distinct().ToList();
+        if (accountIds.Count != 1)
+            return;
+
+        var accountId = accountIds[0];
+        var uniqueIds = targetList.Select(a => a.MailCopy.UniqueId).Distinct().ToList();
+
+        if (isAssignedToAll)
+        {
+            await _mailCategoryService.UnassignCategoryAsync(category.Id, uniqueIds).ConfigureAwait(false);
+        }
+        else
+        {
+            await _mailCategoryService.AssignCategoryAsync(category.Id, uniqueIds).ConfigureAwait(false);
+        }
+
+        if (targetList.First().MailCopy.AssignedAccount.ProviderType != MailProviderType.Outlook)
+            return;
+
+        var requests = new List<IRequestBase>();
+        foreach (var mailItem in targetList.Select(a => a.MailCopy).DistinctBy(a => a.UniqueId))
+        {
+            var categoryNames = await _mailCategoryService.GetCategoryNamesForMailAsync(mailItem.UniqueId).ConfigureAwait(false);
+            requests.Add(new MailCategoryAssignmentRequest(mailItem, category.Id, category.Name, categoryNames, !isAssignedToAll));
+        }
+
+        await _winoRequestDelegator.ExecuteAsync(accountId, requests).ConfigureAwait(false);
+    }
+
     private bool ShouldPreventItemAdd(MailCopy mailItem)
     {
         bool condition = mailItem.IsRead
@@ -691,7 +752,7 @@ public partial class MailListPageViewModel : MailBaseViewModel,
         => ActiveFolder?.SpecialFolderType == SpecialFolderType.Draft;
 
     private bool BelongsToActiveFolder(MailCopy mailItem)
-        => mailItem?.AssignedFolder != null && ActiveFolder?.HandlingFolders?.Any(a => a.Id == mailItem.AssignedFolder.Id) == true;
+        => !IsCategoryView && mailItem?.AssignedFolder != null && ActiveFolder?.HandlingFolders?.Any(a => a.Id == mailItem.AssignedFolder.Id) == true;
 
     private bool ShouldIncludeByThread(MailCopy mailItem)
         => PreferencesService.IsThreadingEnabled
@@ -1069,6 +1130,38 @@ public partial class MailListPageViewModel : MailBaseViewModel,
         }
     }
 
+    private MailListInitializationOptions CreateInitializationOptions(
+        string searchQuery,
+        System.Collections.Concurrent.ConcurrentDictionary<Guid, bool> existingUniqueIds,
+        List<MailCopy> preFetchedMailCopies = null,
+        bool deduplicateByServerId = false)
+    {
+        var options = new MailListInitializationOptions(ActiveFolder.HandlingFolders,
+                                                        SelectedFilterOption.Type,
+                                                        SelectedSortingOption.Type,
+                                                        PreferencesService.IsThreadingEnabled,
+                                                        SelectedFolderPivot.IsFocused,
+                                                        searchQuery,
+                                                        existingUniqueIds,
+                                                        preFetchedMailCopies,
+                                                        DeduplicateByServerId: deduplicateByServerId);
+
+        if (!IsCategoryView)
+            return options;
+
+        var categoryIds = ActiveFolder switch
+        {
+            IMailCategoryMenuItem singleCategoryMenuItem => new List<Guid> { singleCategoryMenuItem.MailCategory.Id },
+            IMergedMailCategoryMenuItem mergedCategoryMenuItem => mergedCategoryMenuItem.Categories.Select(a => a.Id).ToList(),
+            _ => []
+        };
+
+        return options with
+        {
+            CategoryIds = categoryIds
+        };
+    }
+
     [RelayCommand]
     private async Task PerformOnlineSearchAsync()
     {
@@ -1218,15 +1311,11 @@ public partial class MailListPageViewModel : MailBaseViewModel,
                 }
             }
 
-            var initializationOptions = new MailListInitializationOptions(ActiveFolder.HandlingFolders,
+            var initializationOptions = CreateInitializationOptions(
-                                                                          SelectedFilterOption.Type,
+                isDoingOnlineSearch ? string.Empty : SearchQuery,
-                                                                          SelectedSortingOption.Type,
+                MailCollection.MailCopyIdHashSet,
-                                                                          PreferencesService.IsThreadingEnabled,
+                onlineSearchItems,
-                                                                          SelectedFolderPivot.IsFocused,
+                isDoingOnlineSearch);
-                                                                          isDoingOnlineSearch ? string.Empty : SearchQuery,
-                                                                          MailCollection.MailCopyIdHashSet,
-                                                                          onlineSearchItems,
-                                                                          DeduplicateByServerId: isDoingOnlineSearch);
 
             items = await _mailService.FetchMailsAsync(initializationOptions, cancellationToken).ConfigureAwait(false);
 

Wino.Mail.WinUI/App.xaml.cs

@@ -364,6 +364,7 @@ public partial class App : WinoApplication,
         services.AddTransient(typeof(StoragePageViewModel));
         services.AddTransient(typeof(WinoAccountManagementPageViewModel));
         services.AddTransient(typeof(AliasManagementPageViewModel));
+        services.AddTransient(typeof(MailCategoryManagementPageViewModel));
         services.AddTransient(typeof(ContactsPageViewModel));
         services.AddTransient(typeof(SignatureAndEncryptionPageViewModel));
         services.AddTransient(typeof(EmailTemplatesPageViewModel));
@@ -1321,6 +1322,7 @@ public partial class App : WinoApplication,
         return synchronizationType switch
         {
             MailSynchronizationType.Alias => Translator.Exception_FailedToSynchronizeAliases,
+            MailSynchronizationType.Categories => Translator.Exception_FailedToSynchronizeCategories,
             MailSynchronizationType.UpdateProfile => Translator.Exception_FailedToSynchronizeProfileInformation,
             _ => Translator.Exception_FailedToSynchronizeFolders
         };

Wino.Mail.WinUI/Dialogs/EditMailCategoryDialog.xaml

@@ -0,0 +1,60 @@
+<ContentDialog
+    x:Class="Wino.Dialogs.EditMailCategoryDialog"
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+    xmlns:domain="using:Wino.Core.Domain"
+    xmlns:helpers="using:Wino.Helpers"
+    xmlns:mailModels="using:Wino.Core.Domain.Models.MailItem"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    DefaultButton="Primary"
+    PrimaryButtonClick="SaveClicked"
+    PrimaryButtonText="{x:Bind domain:Translator.Buttons_Save, Mode=OneTime}"
+    SecondaryButtonClick="CancelClicked"
+    SecondaryButtonText="{x:Bind domain:Translator.Buttons_Cancel, Mode=OneTime}"
+    Style="{StaticResource WinoDialogStyle}"
+    mc:Ignorable="d">
+
+    <ContentDialog.Resources>
+        <x:Double x:Key="ContentDialogMinWidth">520</x:Double>
+        <x:Double x:Key="ContentDialogMaxWidth">520</x:Double>
+    </ContentDialog.Resources>
+
+    <StackPanel Spacing="16">
+        <TextBox
+            x:Name="CategoryNameTextBox"
+            Header="{x:Bind domain:Translator.MailCategoryDialog_Name, Mode=OneTime}"
+            PlaceholderText="{x:Bind domain:Translator.MailCategoryDialog_NamePlaceholder, Mode=OneTime}"
+            Text="{x:Bind CategoryName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
+            TextChanged="CategoryNameTextChanged" />
+
+        <StackPanel Spacing="8">
+            <TextBlock Style="{StaticResource BodyStrongTextBlockStyle}" Text="{x:Bind domain:Translator.MailCategoryDialog_Color, Mode=OneTime}" />
+
+            <GridView
+                x:Name="ColorsGridView"
+                IsItemClickEnabled="True"
+                ItemClick="ColorOptionClicked"
+                ItemsSource="{x:Bind AvailableColors, Mode=OneWay}"
+                SelectedItem="{x:Bind SelectedColor, Mode=TwoWay}"
+                SelectionMode="Single">
+                <GridView.ItemTemplate>
+                    <DataTemplate x:DataType="mailModels:MailCategoryColorOption">
+                        <Border
+                            Width="100"
+                            Padding="8,6"
+                            Background="{x:Bind helpers:XamlHelpers.GetSolidColorBrushFromHex(BackgroundColorHex), Mode=OneWay}"
+                            BorderBrush="{x:Bind helpers:XamlHelpers.GetSolidColorBrushFromHex(TextColorHex), Mode=OneWay}"
+                            BorderThickness="1"
+                            CornerRadius="10">
+                            <TextBlock
+                                HorizontalAlignment="Center"
+                                Foreground="{x:Bind helpers:XamlHelpers.GetSolidColorBrushFromHex(TextColorHex), Mode=OneWay}"
+                                Text="Preview" />
+                        </Border>
+                    </DataTemplate>
+                </GridView.ItemTemplate>
+            </GridView>
+        </StackPanel>
+    </StackPanel>
+</ContentDialog>

Wino.Mail.WinUI/Dialogs/EditMailCategoryDialog.xaml.cs

@@ -0,0 +1,59 @@
+using System.Linq;
+using Microsoft.UI.Xaml.Controls;
+using Wino.Core.Domain;
+using Wino.Core.Domain.Entities.Mail;
+using Wino.Core.Domain.Models.MailItem;
+
+namespace Wino.Dialogs;
+
+public sealed partial class EditMailCategoryDialog : ContentDialog
+{
+    public MailCategoryDialogResult? Result { get; private set; }
+    public string CategoryName { get; set; }
+    public MailCategoryColorOption? SelectedColor { get; set; }
+
+    public System.Collections.Generic.IReadOnlyList<MailCategoryColorOption> AvailableColors => MailCategoryPalette.DefaultOptions;
+
+    public EditMailCategoryDialog(MailCategory? category = null)
+    {
+        InitializeComponent();
+
+        Title = category == null ? Translator.MailCategoryDialog_CreateTitle : Translator.MailCategoryDialog_EditTitle;
+        CategoryName = category?.Name ?? string.Empty;
+        SelectedColor = MailCategoryPalette.DefaultOptions.FirstOrDefault(a =>
+            a.BackgroundColorHex == category?.BackgroundColorHex &&
+            a.TextColorHex == category?.TextColorHex) ?? MailCategoryPalette.DefaultOptions.First();
+
+        IsPrimaryButtonEnabled = !string.IsNullOrWhiteSpace(CategoryName);
+    }
+
+    private void CategoryNameTextChanged(object sender, TextChangedEventArgs e)
+        => IsPrimaryButtonEnabled = !string.IsNullOrWhiteSpace(CategoryNameTextBox.Text) && SelectedColor != null;
+
+    private void ColorOptionClicked(object sender, ItemClickEventArgs e)
+    {
+        if (e.ClickedItem is MailCategoryColorOption option)
+        {
+            SelectedColor = option;
+            ColorsGridView.SelectedItem = option;
+            IsPrimaryButtonEnabled = !string.IsNullOrWhiteSpace(CategoryNameTextBox.Text);
+        }
+    }
+
+    private void SaveClicked(ContentDialog sender, ContentDialogButtonClickEventArgs args)
+    {
+        if (SelectedColor == null)
+        {
+            args.Cancel = true;
+            return;
+        }
+
+        Result = new MailCategoryDialogResult(CategoryNameTextBox.Text?.Trim(), SelectedColor.BackgroundColorHex, SelectedColor.TextColorHex);
+        Hide();
+    }
+
+    private void CancelClicked(ContentDialog sender, ContentDialogButtonClickEventArgs args)
+    {
+        Hide();
+    }
+}

Wino.Mail.WinUI/Selectors/NavigationMenuTemplateSelector.cs

@@ -26,6 +26,7 @@ public partial class NavigationMenuTemplateSelector : DataTemplateSelector
     public DataTemplate NewMailTemplate { get; set; } = null!;
     public DataTemplate CalendarNewEventTemplate { get; set; } = null!;
     public DataTemplate CategoryItemsTemplate { get; set; } = null!;
+    public DataTemplate MergedCategoryItemsTemplate { get; set; } = null!;
     public DataTemplate FixAuthenticationIssueTemplate { get; set; } = null!;
     public DataTemplate FixMissingFolderConfigTemplate { get; set; } = null!;
 
@@ -58,6 +59,10 @@ public partial class NavigationMenuTemplateSelector : DataTemplateSelector
             return MergedAccountTemplate;
         else if (item is MergedAccountMoreFolderMenuItem)
             return MergedAccountMoreExpansionItemTemplate;
+        else if (item is MailCategoryMenuItem)
+            return CategoryItemsTemplate;
+        else if (item is MergedMailCategoryMenuItem)
+            return MergedCategoryItemsTemplate;
         else if (item is MergedAccountFolderMenuItem)
             return MergedAccountFolderTemplate;
         else if (item is FolderMenuItem)

Wino.Mail.WinUI/Services/DialogService.cs

@@ -6,7 +6,6 @@ using CommunityToolkit.Mvvm.Messaging;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
 using Wino.Core.Domain;
-using Wino.Core.Domain.Entities.Calendar;
 using Wino.Core.Domain.Entities.Mail;
 using Wino.Core.Domain.Entities.Shared;
 using Wino.Core.Domain.Enums;
@@ -15,11 +14,12 @@ using Wino.Core.Domain.Models;
 using Wino.Core.Domain.Models.Accounts;
 using Wino.Core.Domain.Models.Calendar;
 using Wino.Core.Domain.Models.Folders;
+using Wino.Core.Domain.Models.MailItem;
 using Wino.Core.Domain.Models.Synchronization;
-using Wino.Mail.WinUI.Extensions;
-using Wino.Mail.WinUI.Services;
 using Wino.Dialogs;
 using Wino.Mail.Dialogs;
+using Wino.Mail.WinUI.Extensions;
+using Wino.Mail.WinUI.Services;
 using Wino.Messaging.Server;
 using Wino.Messaging.UI;
 
@@ -58,6 +58,19 @@ public class DialogService : DialogServiceBase, IMailDialogService
         return createAccountAliasDialog;
     }
 
+#pragma warning disable CS8625
+    public async Task<MailCategoryDialogResult> ShowEditMailCategoryDialogAsync(MailCategory category = null)
+#pragma warning restore CS8625
+    {
+        var dialog = new EditMailCategoryDialog(category)
+        {
+            RequestedTheme = ThemeService.RootTheme.ToWindowsElementTheme()
+        };
+
+        await HandleDialogPresentationAsync(dialog);
+        return dialog.Result;
+    }
+
     public async Task HandleSystemFolderConfigurationDialogAsync(Guid accountId, IFolderService folderService)
     {
         try

Wino.Mail.WinUI/Services/NavigationService.cs

@@ -82,6 +82,7 @@ public class NavigationService : NavigationServiceBase, INavigationService
         WinoPage.ReadComposePanePage,
         WinoPage.AppPreferencesPage,
         WinoPage.AliasManagementPage,
+        WinoPage.MailCategoryManagementPage,
         WinoPage.ImapCalDavSettingsPage,
         WinoPage.KeyboardShortcutsPage,
         WinoPage.SignatureAndEncryptionPage,
@@ -150,6 +151,7 @@ public class NavigationService : NavigationServiceBase, INavigationService
             WinoPage.SettingOptionsPage => typeof(SettingOptionsPage),
             WinoPage.AppPreferencesPage => typeof(AppPreferencesPage),
             WinoPage.AliasManagementPage => typeof(AliasManagementPage),
+            WinoPage.MailCategoryManagementPage => typeof(MailCategoryManagementPage),
             WinoPage.ImapCalDavSettingsPage => typeof(ImapCalDavSettingsPage),
             WinoPage.KeyboardShortcutsPage => typeof(KeyboardShortcutsPage),
             WinoPage.ContactsPage => typeof(ContactsPage),

Wino.Mail.WinUI/Views/Abstract/MailCategoryManagementPageAbstract.cs

@@ -0,0 +1,6 @@
+using Wino.Mail.ViewModels;
+using Wino.Mail.WinUI;
+
+namespace Wino.Views.Abstract;
+
+public abstract class MailCategoryManagementPageAbstract : BasePage<MailCategoryManagementPageViewModel> { }

Wino.Mail.WinUI/Views/Mail/MailListPage.xaml

@@ -253,7 +253,8 @@
                             BorderThickness="0"
                             Command="{x:Bind ViewModel.SyncFolderCommand}"
                             IsEnabled="{x:Bind ViewModel.CanSynchronize, Mode=OneWay}"
-                            ToolTipService.ToolTip="{x:Bind domain:Translator.Buttons_Sync}">
+                            ToolTipService.ToolTip="{x:Bind domain:Translator.Buttons_Sync}"
+                            Visibility="{x:Bind ViewModel.IsSyncButtonVisible, Mode=OneWay}">
                             <coreControls:WinoFontIcon FontSize="14" Icon="Sync" />
                         </Button>
                         <ToggleButton
@@ -290,9 +291,11 @@
                     </StackPanel>
 
                     <InfoBar
+                        x:Name="SyncDisabledInfoBar"
                         Title="{x:Bind domain:Translator.InfoBarTitle_SynchronizationDisabledFolder}"
                         Grid.Row="0"
                         Grid.ColumnSpan="3"
+                        x:Load="{x:Bind ViewModel.IsSyncButtonVisible, Mode=OneWay}"
                         IsClosable="True"
                         IsOpen="{x:Bind ViewModel.IsFolderSynchronizationEnabled, Converter={StaticResource ReverseBooleanConverter}, Mode=OneWay}"
                         Message="{x:Bind domain:Translator.InfoBarMessage_SynchronizationDisabledFolder}"

Wino.Mail.WinUI/Views/Mail/MailListPage.xaml.cs

@@ -1,6 +1,6 @@
 using System;
-using System.Collections.ObjectModel;
 using System.Collections.Generic;
+using System.Collections.ObjectModel;
 using System.Linq;
 using System.Threading.Tasks;
 using CommunityToolkit.Mvvm.Collections;
@@ -18,6 +18,7 @@ using Windows.Foundation;
 using Windows.System;
 using Wino.Controls;
 using Wino.Core.Domain;
+using Wino.Core.Domain.Entities.Mail;
 using Wino.Core.Domain.Enums;
 using Wino.Core.Domain.Interfaces;
 using Wino.Core.Domain.Models.MailItem;
@@ -27,7 +28,6 @@ using Wino.Mail.ViewModels.Data;
 using Wino.Mail.ViewModels.Messages;
 using Wino.Mail.WinUI;
 using Wino.Mail.WinUI.Controls.ListView;
-using Wino.Mail.WinUI.Extensions;
 using Wino.Mail.WinUI.Helpers;
 using Wino.Mail.WinUI.Interfaces;
 using Wino.Mail.WinUI.Models;
@@ -246,14 +246,27 @@ public sealed partial class MailListPage : MailListPageAbstract,
             // Default to all selected items.
             targetItems = ViewModel.MailCollection.SelectedItems;
             var availableActions = ViewModel.GetAvailableMailActions(targetItems);
+            var (availableCategories, assignedCategoryIds) = await ViewModel.GetAvailableCategoriesAsync(targetItems);
 
             if (availableActions == null || !availableActions.Any()) return;
 
-            var clickedOperation = await GetMailOperationFromFlyoutAsync(availableActions, control, p.X, p.Y);
+            var clickedAction = await GetMailContextActionFromFlyoutAsync(
+                availableActions,
+                availableCategories,
+                assignedCategoryIds,
+                control,
+                p.X,
+                p.Y);
 
-            if (clickedOperation == null) return;
+            if (clickedAction == null) return;
 
-            var prepRequest = new MailOperationPreperationRequest(clickedOperation.Operation, targetItems.Select(a => a.MailCopy));
+            if (clickedAction.Category != null)
+            {
+                await ViewModel.ToggleCategoryAssignmentAsync(clickedAction.Category, targetItems, clickedAction.IsCategoryAssignedToAll);
+                return;
+            }
+
+            var prepRequest = new MailOperationPreperationRequest(clickedAction.Operation.Operation, targetItems.Select(a => a.MailCopy));
 
             await ViewModel.ExecuteMailOperationAsync(prepRequest);
         }
@@ -296,14 +309,68 @@ public sealed partial class MailListPage : MailListPageAbstract,
         });
     }
 
-    private async Task<MailOperationMenuItem> GetMailOperationFromFlyoutAsync(IEnumerable<MailOperationMenuItem> availableActions,
+    private async Task<MailContextAction?> GetMailContextActionFromFlyoutAsync(
-                                                                              UIElement showAtElement,
+        IEnumerable<MailOperationMenuItem> availableActions,
-                                                                              double x,
+        IReadOnlyList<MailCategory> availableCategories,
-                                                                              double y)
+        IReadOnlyCollection<Guid> assignedCategoryIds,
+        UIElement showAtElement,
+        double x,
+        double y)
     {
-        var source = new TaskCompletionSource<MailOperationMenuItem>();
+        var source = new TaskCompletionSource<MailContextAction?>();
+        var flyout = new MenuFlyout();
 
-        var flyout = new MailOperationFlyout(availableActions, source);
+        foreach (var action in availableActions)
+        {
+            if (action.Operation == MailOperation.Seperator)
+            {
+                flyout.Items.Add(new MenuFlyoutSeparator());
+                continue;
+            }
+
+            var menuFlyoutItem = new MailOperationMenuFlyoutItem(action, clicked =>
+            {
+                source.TrySetResult(new MailContextAction(clicked));
+                flyout.Hide();
+            });
+
+            flyout.Items.Add(menuFlyoutItem);
+        }
+
+        if (availableCategories?.Count > 0)
+        {
+            if (flyout.Items.LastOrDefault() is not MenuFlyoutSeparator)
+            {
+                flyout.Items.Add(new MenuFlyoutSeparator());
+            }
+
+            var categorySubItem = new MenuFlyoutSubItem
+            {
+                Text = Translator.MailCategoryMenuItem
+            };
+
+            foreach (var category in availableCategories)
+            {
+                var wasAssignedToAll = assignedCategoryIds.Contains(category.Id);
+                var categoryItem = new ToggleMenuFlyoutItem
+                {
+                    Text = category.Name,
+                    IsChecked = wasAssignedToAll
+                };
+
+                categoryItem.Click += (_, _) =>
+                {
+                    source.TrySetResult(new MailContextAction(category, wasAssignedToAll));
+                    flyout.Hide();
+                };
+
+                categorySubItem.Items.Add(categoryItem);
+            }
+
+            flyout.Items.Add(categorySubItem);
+        }
+
+        flyout.Closing += (_, _) => source.TrySetResult(null);
 
         flyout.ShowAt(showAtElement, new FlyoutShowOptions()
         {
@@ -314,6 +381,13 @@ public sealed partial class MailListPage : MailListPageAbstract,
         return await source.Task;
     }
 
+    private sealed record MailContextAction(MailOperationMenuItem Operation, MailCategory Category = null, bool IsCategoryAssignedToAll = false)
+    {
+        public MailContextAction(MailCategory category, bool isCategoryAssignedToAll) : this(null, category, isCategoryAssignedToAll)
+        {
+        }
+    }
+
     async void IRecipient<ClearMailSelectionsRequested>.Receive(ClearMailSelectionsRequested message)
     {
         await ViewModel.MailCollection.UnselectAllAsync();

Wino.Mail.WinUI/Views/Settings/MailCategoryManagementPage.xaml

@@ -0,0 +1,169 @@
+<abstract:MailCategoryManagementPageAbstract
+    x:Class="Wino.Views.Settings.MailCategoryManagementPage"
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:abstract="using:Wino.Views.Abstract"
+    xmlns:controls="using:Wino.Controls"
+    xmlns:coreControls="using:Wino.Mail.WinUI.Controls"
+    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+    xmlns:domain="using:Wino.Core.Domain"
+    xmlns:helpers="using:Wino.Helpers"
+    xmlns:mail="using:Wino.Core.Domain.Entities.Mail"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    x:Name="root"
+    mc:Ignorable="d">
+
+    <Page.Resources>
+        <DataTemplate x:Key="MailCategoryTemplate" x:DataType="mail:MailCategory">
+            <Grid
+                Margin="0,0,0,12"
+                Padding="0,0,0,12"
+                ColumnSpacing="16">
+                <Grid.ColumnDefinitions>
+                    <ColumnDefinition Width="*" />
+                    <ColumnDefinition Width="Auto" />
+                    <ColumnDefinition Width="Auto" />
+                    <ColumnDefinition Width="Auto" />
+                    <ColumnDefinition Width="Auto" />
+                </Grid.ColumnDefinitions>
+
+                <Grid
+                    VerticalAlignment="Center"
+                    ColumnSpacing="12">
+                    <Grid.ColumnDefinitions>
+                        <ColumnDefinition Width="Auto" />
+                        <ColumnDefinition Width="*" />
+                    </Grid.ColumnDefinitions>
+
+                    <Border
+                        Width="28"
+                        Height="28"
+                        VerticalAlignment="Top"
+                        Background="{x:Bind helpers:XamlHelpers.GetSolidColorBrushFromHex(BackgroundColorHex), Mode=OneWay}"
+                        BorderBrush="{x:Bind helpers:XamlHelpers.GetSolidColorBrushFromHex(TextColorHex), Mode=OneWay}"
+                        BorderThickness="1"
+                        CornerRadius="8" />
+
+                    <StackPanel
+                        Grid.Column="1"
+                        VerticalAlignment="Center"
+                        Spacing="2">
+                        <TextBlock
+                            FontWeight="SemiBold"
+                            Foreground="{x:Bind helpers:XamlHelpers.GetSolidColorBrushFromHex(TextColorHex), Mode=OneWay}"
+                            Style="{StaticResource BodyTextBlockStyle}"
+                            Text="{x:Bind Name}"
+                            TextTrimming="CharacterEllipsis" />
+                        <TextBlock
+                            Foreground="{ThemeResource TextFillColorSecondaryBrush}"
+                            Style="{StaticResource CaptionTextBlockStyle}">
+                            <Run Text="{x:Bind BackgroundColorHex}" />
+                            <Run Text=" / " />
+                            <Run Text="{x:Bind TextColorHex}" />
+                        </TextBlock>
+                    </StackPanel>
+                </Grid>
+
+                <ToggleButton
+                    Grid.Column="1"
+                    Checked="FavoriteCategoryChecked"
+                    IsChecked="{x:Bind IsFavorite, Mode=OneWay}"
+                    Tag="{x:Bind}"
+                    Unchecked="FavoriteCategoryUnchecked">
+                    <FontIcon FontFamily="{StaticResource SymbolThemeFontFamily}" Glyph="&#xE208;" />
+                </ToggleButton>
+
+                <Button
+                    Grid.Column="2"
+                    Click="EditCategoryClicked"
+                    Tag="{x:Bind}">
+                    <FontIcon FontFamily="{StaticResource SymbolThemeFontFamily}" Glyph="&#xE70F;" />
+                </Button>
+
+                <Button
+                    Grid.Column="3"
+                    Click="DeleteCategoryClicked"
+                    Tag="{x:Bind}">
+                    <FontIcon FontFamily="{StaticResource SymbolThemeFontFamily}" Glyph="&#xE74D;" />
+                </Button>
+
+                <Rectangle
+                    Grid.ColumnSpan="5"
+                    Height="1"
+                    Margin="0,12,0,0"
+                    VerticalAlignment="Bottom"
+                    Fill="{ThemeResource CardStrokeColorDefaultBrush}" />
+            </Grid>
+        </DataTemplate>
+    </Page.Resources>
+
+    <ListView
+        ItemTemplate="{StaticResource MailCategoryTemplate}"
+        ItemsSource="{x:Bind ViewModel.Categories, Mode=OneWay}"
+        SelectionMode="None">
+        <ListView.ItemContainerTransitions>
+            <TransitionCollection>
+                <NavigationThemeTransition />
+            </TransitionCollection>
+        </ListView.ItemContainerTransitions>
+        <ListView.Header>
+            <Grid
+                Padding="16,0,24,20"
+                ColumnSpacing="16">
+                <Grid.ColumnDefinitions>
+                    <ColumnDefinition Width="*" />
+                    <ColumnDefinition Width="Auto" />
+                    <ColumnDefinition Width="Auto" />
+                </Grid.ColumnDefinitions>
+
+                <Grid Style="{StaticResource InformationAreaGridStyle}">
+                    <TextBlock HorizontalTextAlignment="Center" TextWrapping="WrapWholeWords">
+                        <Run FontWeight="SemiBold" Text="{x:Bind domain:Translator.MailCategoryManagementPage_Title, Mode=OneTime}" />
+                        <LineBreak />
+                        <Run Text="{x:Bind domain:Translator.MailCategoryManagementPage_Description, Mode=OneTime}" />
+                    </TextBlock>
+                </Grid>
+
+                <Button
+                    Grid.Column="1"
+                    HorizontalAlignment="Stretch"
+                    VerticalAlignment="Stretch"
+                    Command="{x:Bind ViewModel.RefreshCategoriesCommand}"
+                    Visibility="{x:Bind ViewModel.CanRefresh, Mode=OneWay}">
+                    <StackPanel Spacing="6">
+                        <FontIcon
+                            HorizontalAlignment="Center"
+                            Glyph="&#xE72C;" />
+                        <TextBlock
+                            HorizontalAlignment="Center"
+                            Text="{x:Bind domain:Translator.Buttons_Refresh, Mode=OneTime}" />
+                    </StackPanel>
+                </Button>
+
+                <Button
+                    Grid.Column="2"
+                    HorizontalAlignment="Stretch"
+                    VerticalAlignment="Stretch"
+                    Command="{x:Bind ViewModel.AddCategoryCommand}">
+                    <StackPanel Spacing="6">
+                        <FontIcon
+                            HorizontalAlignment="Center"
+                            Glyph="&#xE710;" />
+                        <TextBlock
+                            HorizontalAlignment="Center"
+                            Text="{x:Bind domain:Translator.Buttons_Add, Mode=OneTime}" />
+                    </StackPanel>
+                </Button>
+            </Grid>
+        </ListView.Header>
+        <ListView.Footer>
+            <TextBlock
+                Margin="0,12,0,0"
+                HorizontalAlignment="Center"
+                Foreground="{ThemeResource TextFillColorSecondaryBrush}"
+                Style="{StaticResource BodyTextBlockStyle}"
+                Text="{x:Bind domain:Translator.MailCategoryManagementPage_Empty, Mode=OneTime}"
+                Visibility="{x:Bind helpers:XamlHelpers.ReverseBoolToVisibilityConverter(ViewModel.HasCategories), Mode=OneWay}" />
+        </ListView.Footer>
+    </ListView>
+</abstract:MailCategoryManagementPageAbstract>

Wino.Mail.WinUI/Views/Settings/MailCategoryManagementPage.xaml.cs

@@ -0,0 +1,47 @@
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+using Microsoft.UI.Xaml.Controls.Primitives;
+using Wino.Core.Domain.Entities.Mail;
+using Wino.Views.Abstract;
+
+namespace Wino.Views.Settings;
+
+public sealed partial class MailCategoryManagementPage : MailCategoryManagementPageAbstract
+{
+    public MailCategoryManagementPage()
+    {
+        InitializeComponent();
+    }
+
+    private async void FavoriteCategoryChecked(object sender, RoutedEventArgs e)
+    {
+        if (sender is ToggleButton toggleButton && toggleButton.Tag is MailCategory category)
+        {
+            await ViewModel.SetFavoriteAsync(category, true);
+        }
+    }
+
+    private async void FavoriteCategoryUnchecked(object sender, RoutedEventArgs e)
+    {
+        if (sender is ToggleButton toggleButton && toggleButton.Tag is MailCategory category)
+        {
+            await ViewModel.SetFavoriteAsync(category, false);
+        }
+    }
+
+    private async void EditCategoryClicked(object sender, RoutedEventArgs e)
+    {
+        if (sender is Button button && button.Tag is MailCategory category)
+        {
+            await ViewModel.EditCategoryAsync(category);
+        }
+    }
+
+    private async void DeleteCategoryClicked(object sender, RoutedEventArgs e)
+    {
+        if (sender is Button button && button.Tag is MailCategory category)
+        {
+            await ViewModel.DeleteCategoryAsync(category);
+        }
+    }
+}

Wino.Mail.WinUI/Views/WinoAppShell.xaml

@@ -240,6 +240,93 @@
             </coreControls:WinoNavigationViewItem>
         </DataTemplate>
 
+        <DataTemplate x:Key="MailCategoryMenuTemplate" x:DataType="menu:MailCategoryMenuItem">
+            <coreControls:WinoNavigationViewItem
+                MinHeight="40"
+                DataContext="{x:Bind}"
+                FontWeight="{x:Bind helpers:XamlHelpers.GetFontWeightByChildSelectedState(IsSelected), Mode=OneWay}"
+                IsSelected="{x:Bind IsSelected, Mode=TwoWay}"
+                SelectsOnInvoked="True"
+                ToolTipService.ToolTip="{x:Bind FolderName, Mode=OneWay}">
+                <muxc:NavigationViewItem.Icon>
+                    <FontIcon
+                        FontFamily="{StaticResource SymbolThemeFontFamily}"
+                        Foreground="{x:Bind helpers:XamlHelpers.GetSolidColorBrushFromHex(BackgroundColorHex), Mode=OneWay}"
+                        Glyph="&#xE8EC;" />
+                </muxc:NavigationViewItem.Icon>
+                <muxc:NavigationViewItem.InfoBadge>
+                    <muxc:InfoBadge
+                        Background="{StaticResource SystemAccentColor}"
+                        Foreground="White"
+                        Visibility="{x:Bind helpers:XamlHelpers.CountToVisibilityConverter(UnreadItemCount), Mode=OneWay}"
+                        Value="{x:Bind UnreadItemCount, Mode=OneWay}" />
+                </muxc:NavigationViewItem.InfoBadge>
+                <muxc:NavigationViewItem.Content>
+                    <TextBlock
+                        Grid.Column="1"
+                        VerticalAlignment="Center"
+                        FontWeight="{x:Bind helpers:XamlHelpers.GetFontWeightBySyncState(IsSelected), Mode=OneWay}"
+                        Style="{StaticResource BodyTextBlockStyle}"
+                        Text="{x:Bind FolderName, Mode=OneWay}"
+                        TextTrimming="CharacterEllipsis" />
+                </muxc:NavigationViewItem.Content>
+            </coreControls:WinoNavigationViewItem>
+        </DataTemplate>
+
+        <DataTemplate x:Key="MergedMailCategoryMenuTemplate" x:DataType="menu:MergedMailCategoryMenuItem">
+            <coreControls:WinoNavigationViewItem
+                MinHeight="40"
+                DataContext="{x:Bind}"
+                FontWeight="{x:Bind helpers:XamlHelpers.GetFontWeightByChildSelectedState(IsSelected), Mode=OneWay}"
+                IsSelected="{x:Bind IsSelected, Mode=TwoWay}"
+                SelectsOnInvoked="True"
+                ToolTipService.ToolTip="{x:Bind FolderName, Mode=OneWay}">
+                <muxc:NavigationViewItem.Icon>
+                    <FontIcon
+                        FontFamily="{StaticResource SymbolThemeFontFamily}"
+                        Foreground="{x:Bind helpers:XamlHelpers.GetSolidColorBrushFromHex(TextColorHex), Mode=OneWay}"
+                        Glyph="&#xE8EC;" />
+                </muxc:NavigationViewItem.Icon>
+                <muxc:NavigationViewItem.InfoBadge>
+                    <muxc:InfoBadge
+                        Background="{StaticResource SystemAccentColor}"
+                        Foreground="White"
+                        Visibility="{x:Bind helpers:XamlHelpers.CountToVisibilityConverter(UnreadItemCount), Mode=OneWay}"
+                        Value="{x:Bind UnreadItemCount, Mode=OneWay}" />
+                </muxc:NavigationViewItem.InfoBadge>
+                <muxc:NavigationViewItem.Content>
+                    <Grid
+                        MaxHeight="36"
+                        Padding="2"
+                        VerticalAlignment="Center">
+                        <Grid.ColumnDefinitions>
+                            <ColumnDefinition Width="Auto" />
+                            <ColumnDefinition Width="*" />
+                        </Grid.ColumnDefinitions>
+
+                        <Border
+                            Width="10"
+                            Height="10"
+                            Margin="0,0,8,0"
+                            VerticalAlignment="Center"
+                            Background="{x:Bind helpers:XamlHelpers.GetSolidColorBrushFromHex(BackgroundColorHex), Mode=OneWay}"
+                            BorderBrush="{x:Bind helpers:XamlHelpers.GetSolidColorBrushFromHex(TextColorHex), Mode=OneWay}"
+                            BorderThickness="1"
+                            CornerRadius="3" />
+
+                        <TextBlock
+                            Grid.Column="1"
+                            VerticalAlignment="Center"
+                            FontWeight="{x:Bind helpers:XamlHelpers.GetFontWeightBySyncState(IsSelected), Mode=OneWay}"
+                            Foreground="{x:Bind helpers:XamlHelpers.GetSolidColorBrushFromHex(TextColorHex), Mode=OneWay}"
+                            Style="{StaticResource BodyTextBlockStyle}"
+                            Text="{x:Bind FolderName, Mode=OneWay}"
+                            TextTrimming="CharacterEllipsis" />
+                    </Grid>
+                </muxc:NavigationViewItem.Content>
+            </coreControls:WinoNavigationViewItem>
+        </DataTemplate>
+
         <!--  Merged Inbox  -->
         <DataTemplate x:Key="MergedAccountTemplate" x:DataType="menu:MergedAccountMenuItem">
             <controls:AccountNavigationItem
@@ -393,6 +480,7 @@
 
         <coreSelectors:NavigationMenuTemplateSelector
             x:Key="NavigationMenuTemplateSelector"
+            CategoryItemsTemplate="{StaticResource MailCategoryMenuTemplate}"
             ClickableAccountMenuTemplate="{StaticResource ClickableAccountMenuTemplate}"
             FixAuthenticationIssueTemplate="{StaticResource FixAuthenticationIssueTemplate}"
             FixMissingFolderConfigTemplate="{StaticResource FixMissingFolderConfig}"
@@ -400,6 +488,7 @@
             MergedAccountFolderTemplate="{StaticResource MergedAccountFolderMenuItemTemplate}"
             MergedAccountMoreExpansionItemTemplate="{StaticResource MergedAccountMoreFolderItemTemplate}"
             MergedAccountTemplate="{StaticResource MergedAccountTemplate}"
+            MergedCategoryItemsTemplate="{StaticResource MergedMailCategoryMenuTemplate}"
             NewMailTemplate="{StaticResource CreateNewMailTemplate}"
             RatingItemTemplate="{StaticResource RatingItemTemplate}"
             SeperatorTemplate="{StaticResource SeperatorTemplate}"

Wino.Services/DatabaseService.cs

@@ -49,6 +49,8 @@ public class DatabaseService : IDatabaseService
     {
         await Task.WhenAll(
             Connection.CreateTableAsync<MailCopy>(),
+            Connection.CreateTableAsync<MailCategory>(),
+            Connection.CreateTableAsync<MailCategoryAssignment>(),
             Connection.CreateTableAsync<MailItemFolder>(),
             Connection.CreateTableAsync<MailAccount>(),
             Connection.CreateTableAsync<AccountContact>(),
@@ -226,6 +228,12 @@ SET {nameof(KeyboardShortcut.Action)} =
         await Connection.ExecuteAsync("CREATE INDEX IF NOT EXISTS IX_MailCopy_MessageId ON MailCopy(MessageId)").ConfigureAwait(false);
         await Connection.ExecuteAsync("CREATE INDEX IF NOT EXISTS IX_MailCopy_FolderId_IsRead ON MailCopy(FolderId, IsRead)").ConfigureAwait(false);
         await Connection.ExecuteAsync("CREATE INDEX IF NOT EXISTS IX_MailCopy_CreationDate ON MailCopy(CreationDate)").ConfigureAwait(false);
+        await Connection.ExecuteAsync("CREATE INDEX IF NOT EXISTS IX_MailCategory_MailAccountId ON MailCategory(MailAccountId)").ConfigureAwait(false);
+        await Connection.ExecuteAsync("CREATE INDEX IF NOT EXISTS IX_MailCategory_MailAccountId_Name ON MailCategory(MailAccountId, Name)").ConfigureAwait(false);
+        await Connection.ExecuteAsync("CREATE INDEX IF NOT EXISTS IX_MailCategory_MailAccountId_IsFavorite ON MailCategory(MailAccountId, IsFavorite)").ConfigureAwait(false);
+        await Connection.ExecuteAsync("CREATE INDEX IF NOT EXISTS IX_MailCategoryAssignment_MailCategoryId ON MailCategoryAssignment(MailCategoryId)").ConfigureAwait(false);
+        await Connection.ExecuteAsync("CREATE INDEX IF NOT EXISTS IX_MailCategoryAssignment_MailCopyUniqueId ON MailCategoryAssignment(MailCopyUniqueId)").ConfigureAwait(false);
+        await Connection.ExecuteAsync("CREATE UNIQUE INDEX IF NOT EXISTS IX_MailCategoryAssignment_Category_MailCopy ON MailCategoryAssignment(MailCategoryId, MailCopyUniqueId)").ConfigureAwait(false);
 
         await Connection.ExecuteAsync("CREATE INDEX IF NOT EXISTS IX_MailItemFolder_MailAccountId ON MailItemFolder(MailAccountId)").ConfigureAwait(false);
         await Connection.ExecuteAsync("CREATE INDEX IF NOT EXISTS IX_MailItemFolder_MailAccountId_RemoteFolderId ON MailItemFolder(MailAccountId, RemoteFolderId)").ConfigureAwait(false);

Wino.Services/FolderService.cs

@@ -22,6 +22,7 @@ namespace Wino.Services;
 public class FolderService : BaseDatabaseService, IFolderService
 {
     private readonly IAccountService _accountService;
+    private readonly IMailCategoryService _mailCategoryService;
     private readonly ILogger _logger = Log.ForContext<FolderService>();
 
     private readonly SpecialFolderType[] gmailCategoryFolderTypes =
@@ -34,9 +35,11 @@ public class FolderService : BaseDatabaseService, IFolderService
     ];
 
     public FolderService(IDatabaseService databaseService,
-                           IAccountService accountService) : base(databaseService)
+                           IAccountService accountService,
+                           IMailCategoryService mailCategoryService) : base(databaseService)
     {
         _accountService = accountService;
+        _mailCategoryService = mailCategoryService;
     }
 
     public async Task ChangeStickyStatusAsync(Guid folderId, bool isSticky)
@@ -269,6 +272,9 @@ public class FolderService : BaseDatabaseService, IFolderService
             }
         }
 
+        var favoriteCategories = await GetFavoriteCategoryMenuItemsAsync(mailAccount, folders, accountMenuItem).ConfigureAwait(false);
+        preparedFolderMenuItems.AddRange(favoriteCategories);
+
         // Only add category folder if it's Gmail.
         if (mailAccount.ProviderType == MailProviderType.Gmail) preparedFolderMenuItems.Add(categoryFolderMenuItem);
 
@@ -309,9 +315,62 @@ public class FolderService : BaseDatabaseService, IFolderService
             preparedFolderMenuItems.Add(menuItem);
         }
 
+        var favoriteCategories = await GetMergedFavoriteCategoryMenuItemsAsync(holdingAccounts, allAccountFolders, mergedAccountFolderMenuItem.Parameter).ConfigureAwait(false);
+        preparedFolderMenuItems.AddRange(favoriteCategories);
+
         return preparedFolderMenuItems;
     }
 
+    private async Task<IEnumerable<IMenuItem>> GetFavoriteCategoryMenuItemsAsync(MailAccount account, IEnumerable<IMailItemFolder> handlingFolders, IMenuItem parentMenuItem)
+    {
+        var favoriteCategories = await _mailCategoryService.GetFavoriteCategoriesAsync(account.Id).ConfigureAwait(false);
+
+        if (!favoriteCategories.Any())
+            return [];
+
+        var availableFolders = handlingFolders
+            .Where(a => a.IsMoveTarget)
+            .Cast<IMailItemFolder>()
+            .ToList();
+
+        return favoriteCategories
+            .Select(category => (IMenuItem)new MailCategoryMenuItem(category, account, availableFolders, parentMenuItem))
+            .ToList();
+    }
+
+    private async Task<IEnumerable<IMenuItem>> GetMergedFavoriteCategoryMenuItemsAsync(IEnumerable<MailAccount> holdingAccounts, IEnumerable<IEnumerable<MailItemFolder>> allAccountFolders, MergedInbox mergedInbox)
+    {
+        var categoriesByAccount = new List<(MailAccount Account, List<MailCategory> Categories)>();
+
+        foreach (var account in holdingAccounts)
+        {
+            var categories = await _mailCategoryService.GetFavoriteCategoriesAsync(account.Id).ConfigureAwait(false);
+            if (categories.Any())
+            {
+                categoriesByAccount.Add((account, categories));
+            }
+        }
+
+        if (!categoriesByAccount.Any())
+            return [];
+
+        var handlingFolders = allAccountFolders
+            .SelectMany(a => a)
+            .Where(a => a.IsMoveTarget)
+            .Cast<IMailItemFolder>()
+            .ToList();
+
+        return categoriesByAccount
+            .SelectMany(a => a.Categories)
+            .GroupBy(a => NormalizeCategoryName(a.Name), StringComparer.OrdinalIgnoreCase)
+            .Select(group => (IMenuItem)new MergedMailCategoryMenuItem(group.ToList(), handlingFolders, mergedInbox))
+            .OrderBy(item => ((MergedMailCategoryMenuItem)item).FolderName, StringComparer.CurrentCultureIgnoreCase)
+            .ToList();
+    }
+
+    private static string NormalizeCategoryName(string name)
+        => name?.Trim() ?? string.Empty;
+
     private HashSet<SpecialFolderType> FindCommonFolders(List<List<MailItemFolder>> lists)
     {
         var allSpecialTypesExceptOther = Enum.GetValues<SpecialFolderType>().Cast<SpecialFolderType>().Where(a => a != SpecialFolderType.Other).ToList();

Wino.Services/MailCategoryService.cs

@@ -0,0 +1,358 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using CommunityToolkit.Mvvm.Messaging;
+using Wino.Core.Domain.Entities.Mail;
+using Wino.Core.Domain.Interfaces;
+using Wino.Core.Domain.Models.Accounts;
+using Wino.Messaging.Client.Accounts;
+using Wino.Messaging.UI;
+
+namespace Wino.Services;
+
+public class MailCategoryService : BaseDatabaseService, IMailCategoryService
+{
+    public MailCategoryService(IDatabaseService databaseService) : base(databaseService)
+    {
+    }
+
+    public Task<List<MailCategory>> GetCategoriesAsync(Guid accountId)
+        => Connection.QueryAsync<MailCategory>(
+            $"SELECT * FROM {nameof(MailCategory)} WHERE {nameof(MailCategory.MailAccountId)} = ? ORDER BY {nameof(MailCategory.IsFavorite)} DESC, {nameof(MailCategory.Name)} COLLATE NOCASE",
+            accountId);
+
+    public Task<List<MailCategory>> GetFavoriteCategoriesAsync(Guid accountId)
+        => Connection.QueryAsync<MailCategory>(
+            $"SELECT * FROM {nameof(MailCategory)} WHERE {nameof(MailCategory.MailAccountId)} = ? AND {nameof(MailCategory.IsFavorite)} = 1 ORDER BY {nameof(MailCategory.Name)} COLLATE NOCASE",
+            accountId);
+
+    public Task<MailCategory> GetCategoryAsync(Guid categoryId)
+        => Connection.FindAsync<MailCategory>(categoryId);
+
+    public async Task<bool> CategoryNameExistsAsync(Guid accountId, string name, Guid? excludedCategoryId = null)
+    {
+        var normalizedName = NormalizeCategoryName(name);
+        if (string.IsNullOrWhiteSpace(normalizedName))
+            return false;
+
+        var sql = $"SELECT COUNT(*) FROM {nameof(MailCategory)} WHERE {nameof(MailCategory.MailAccountId)} = ? AND lower(trim({nameof(MailCategory.Name)})) = ?";
+        var parameters = new List<object> { accountId, normalizedName.ToLowerInvariant() };
+
+        if (excludedCategoryId.HasValue)
+        {
+            sql += $" AND {nameof(MailCategory.Id)} <> ?";
+            parameters.Add(excludedCategoryId.Value);
+        }
+
+        return await Connection.ExecuteScalarAsync<int>(sql, parameters.ToArray()).ConfigureAwait(false) > 0;
+    }
+
+    public async Task<MailCategory> CreateCategoryAsync(MailCategory category)
+    {
+        category.Id = category.Id == Guid.Empty ? Guid.NewGuid() : category.Id;
+        category.Name = NormalizeCategoryName(category.Name);
+
+        await Connection.InsertAsync(category, typeof(MailCategory)).ConfigureAwait(false);
+        NotifyCategoryStructureChanged(category.MailAccountId);
+
+        return category;
+    }
+
+    public async Task UpdateCategoryAsync(MailCategory category)
+    {
+        category.Name = NormalizeCategoryName(category.Name);
+
+        await Connection.UpdateAsync(category, typeof(MailCategory)).ConfigureAwait(false);
+        NotifyCategoryStructureChanged(category.MailAccountId);
+    }
+
+    public async Task DeleteCategoryAsync(Guid categoryId)
+    {
+        var category = await GetCategoryAsync(categoryId).ConfigureAwait(false);
+        if (category == null)
+            return;
+
+        await Connection.ExecuteAsync($"DELETE FROM {nameof(MailCategoryAssignment)} WHERE {nameof(MailCategoryAssignment.MailCategoryId)} = ?", categoryId).ConfigureAwait(false);
+        await Connection.DeleteAsync<MailCategory>(categoryId).ConfigureAwait(false);
+
+        NotifyCategoryStructureChanged(category.MailAccountId);
+    }
+
+    public async Task DeleteCategoriesAsync(Guid accountId)
+    {
+        var categories = await GetCategoriesAsync(accountId).ConfigureAwait(false);
+
+        if (categories.Count == 0)
+            return;
+
+        var categoryIds = categories.Select(a => a.Id).ToList();
+        var placeholders = string.Join(",", categoryIds.Select(_ => "?"));
+        var deleteAssignmentsSql = $"DELETE FROM {nameof(MailCategoryAssignment)} WHERE {nameof(MailCategoryAssignment.MailCategoryId)} IN ({placeholders})";
+
+        await Connection.ExecuteAsync(deleteAssignmentsSql, categoryIds.Cast<object>().ToArray()).ConfigureAwait(false);
+        await Connection.Table<MailCategory>().DeleteAsync(a => a.MailAccountId == accountId).ConfigureAwait(false);
+
+        NotifyCategoryStructureChanged(accountId);
+    }
+
+    public async Task ToggleFavoriteAsync(Guid categoryId, bool isFavorite)
+    {
+        var category = await GetCategoryAsync(categoryId).ConfigureAwait(false);
+        if (category == null || category.IsFavorite == isFavorite)
+            return;
+
+        category.IsFavorite = isFavorite;
+        await Connection.UpdateAsync(category, typeof(MailCategory)).ConfigureAwait(false);
+
+        NotifyCategoryStructureChanged(category.MailAccountId);
+    }
+
+    public async Task UpdateRemoteIdAsync(Guid categoryId, string remoteId)
+    {
+        var category = await GetCategoryAsync(categoryId).ConfigureAwait(false);
+        if (category == null)
+            return;
+
+        category.RemoteId = remoteId;
+        await Connection.UpdateAsync(category, typeof(MailCategory)).ConfigureAwait(false);
+    }
+
+    public async Task ReplaceCategoriesAsync(Guid accountId, IEnumerable<MailCategory> categories)
+    {
+        var existingCategories = await GetCategoriesAsync(accountId).ConfigureAwait(false);
+        var existingByRemoteId = existingCategories
+            .Where(a => !string.IsNullOrWhiteSpace(a.RemoteId))
+            .ToDictionary(a => a.RemoteId, StringComparer.OrdinalIgnoreCase);
+        var existingByName = existingCategories
+            .GroupBy(a => NormalizeCategoryName(a.Name), StringComparer.OrdinalIgnoreCase)
+            .ToDictionary(a => a.Key, a => a.First(), StringComparer.OrdinalIgnoreCase);
+
+        var incomingCategories = categories?.ToList() ?? [];
+        var preservedIds = new HashSet<Guid>();
+
+        foreach (var incoming in incomingCategories)
+        {
+            incoming.MailAccountId = accountId;
+            incoming.Id = incoming.Id == Guid.Empty ? Guid.NewGuid() : incoming.Id;
+            incoming.Name = NormalizeCategoryName(incoming.Name);
+
+            MailCategory existing = null;
+
+            if (!string.IsNullOrWhiteSpace(incoming.RemoteId) && existingByRemoteId.TryGetValue(incoming.RemoteId, out var byRemote))
+            {
+                existing = byRemote;
+            }
+            else if (existingByName.TryGetValue(incoming.Name, out var byName))
+            {
+                existing = byName;
+            }
+
+            if (existing == null)
+            {
+                await Connection.InsertAsync(incoming, typeof(MailCategory)).ConfigureAwait(false);
+                preservedIds.Add(incoming.Id);
+            }
+            else
+            {
+                incoming.Id = existing.Id;
+                incoming.IsFavorite = existing.IsFavorite;
+                await Connection.UpdateAsync(incoming, typeof(MailCategory)).ConfigureAwait(false);
+                preservedIds.Add(existing.Id);
+            }
+        }
+
+        var categoryIdsToDelete = existingCategories
+            .Where(a => !preservedIds.Contains(a.Id))
+            .Select(a => a.Id)
+            .ToList();
+
+        if (categoryIdsToDelete.Count > 0)
+        {
+            var placeholders = string.Join(",", categoryIdsToDelete.Select(_ => "?"));
+            await Connection.ExecuteAsync(
+                $"DELETE FROM {nameof(MailCategoryAssignment)} WHERE {nameof(MailCategoryAssignment.MailCategoryId)} IN ({placeholders})",
+                categoryIdsToDelete.Cast<object>().ToArray()).ConfigureAwait(false);
+
+            foreach (var categoryId in categoryIdsToDelete)
+            {
+                await Connection.DeleteAsync<MailCategory>(categoryId).ConfigureAwait(false);
+            }
+        }
+
+        NotifyCategoryStructureChanged(accountId);
+    }
+
+    public async Task ReplaceMailAssignmentsAsync(Guid accountId, Guid mailCopyUniqueId, IEnumerable<string> categoryNames)
+    {
+        var normalizedNames = categoryNames?
+            .Select(NormalizeCategoryName)
+            .Where(a => !string.IsNullOrWhiteSpace(a))
+            .Distinct(StringComparer.OrdinalIgnoreCase)
+            .ToList() ?? [];
+
+        var availableCategories = await GetCategoriesAsync(accountId).ConfigureAwait(false);
+        var categoryIds = availableCategories
+            .Where(a => normalizedNames.Contains(NormalizeCategoryName(a.Name), StringComparer.OrdinalIgnoreCase))
+            .Select(a => a.Id)
+            .ToHashSet();
+
+        var existingAssignments = await Connection.QueryAsync<MailCategoryAssignment>(
+            $"SELECT * FROM {nameof(MailCategoryAssignment)} WHERE {nameof(MailCategoryAssignment.MailCopyUniqueId)} = ?",
+            mailCopyUniqueId).ConfigureAwait(false);
+
+        var assignmentsToDelete = existingAssignments.Where(a => !categoryIds.Contains(a.MailCategoryId)).ToList();
+        var existingIds = existingAssignments.Select(a => a.MailCategoryId).ToHashSet();
+        var assignmentsToAdd = categoryIds.Where(a => !existingIds.Contains(a)).ToList();
+
+        foreach (var assignment in assignmentsToDelete)
+        {
+            await Connection.DeleteAsync<MailCategoryAssignment>(assignment.Id).ConfigureAwait(false);
+        }
+
+        foreach (var categoryId in assignmentsToAdd)
+        {
+            await Connection.InsertAsync(new MailCategoryAssignment
+            {
+                Id = Guid.NewGuid(),
+                MailCategoryId = categoryId,
+                MailCopyUniqueId = mailCopyUniqueId
+            }, typeof(MailCategoryAssignment)).ConfigureAwait(false);
+        }
+
+        WeakReferenceMessenger.Default.Send(new RefreshUnreadCountsMessage(accountId));
+    }
+
+    public async Task AssignCategoryAsync(Guid categoryId, IEnumerable<Guid> mailCopyUniqueIds)
+    {
+        var uniqueIds = mailCopyUniqueIds?.Distinct().ToList() ?? [];
+        if (uniqueIds.Count == 0)
+            return;
+
+        var category = await GetCategoryAsync(categoryId).ConfigureAwait(false);
+        if (category == null)
+            return;
+
+        var placeholders = string.Join(",", uniqueIds.Select(_ => "?"));
+        var query = $"SELECT * FROM {nameof(MailCategoryAssignment)} WHERE {nameof(MailCategoryAssignment.MailCategoryId)} = ? AND {nameof(MailCategoryAssignment.MailCopyUniqueId)} IN ({placeholders})";
+        var existingAssignments = await Connection.QueryAsync<MailCategoryAssignment>(
+            query,
+            [categoryId, .. uniqueIds.Cast<object>()]).ConfigureAwait(false);
+        var existingUniqueIds = existingAssignments.Select(a => a.MailCopyUniqueId).ToHashSet();
+
+        foreach (var uniqueId in uniqueIds.Where(a => !existingUniqueIds.Contains(a)))
+        {
+            await Connection.InsertAsync(new MailCategoryAssignment
+            {
+                Id = Guid.NewGuid(),
+                MailCategoryId = categoryId,
+                MailCopyUniqueId = uniqueId
+            }, typeof(MailCategoryAssignment)).ConfigureAwait(false);
+        }
+
+        WeakReferenceMessenger.Default.Send(new RefreshUnreadCountsMessage(category.MailAccountId));
+    }
+
+    public async Task UnassignCategoryAsync(Guid categoryId, IEnumerable<Guid> mailCopyUniqueIds)
+    {
+        var uniqueIds = mailCopyUniqueIds?.Distinct().ToList() ?? [];
+        if (uniqueIds.Count == 0)
+            return;
+
+        var category = await GetCategoryAsync(categoryId).ConfigureAwait(false);
+        if (category == null)
+            return;
+
+        var placeholders = string.Join(",", uniqueIds.Select(_ => "?"));
+        await Connection.ExecuteAsync(
+            $"DELETE FROM {nameof(MailCategoryAssignment)} WHERE {nameof(MailCategoryAssignment.MailCategoryId)} = ? AND {nameof(MailCategoryAssignment.MailCopyUniqueId)} IN ({placeholders})",
+            [categoryId, .. uniqueIds.Cast<object>()]).ConfigureAwait(false);
+
+        WeakReferenceMessenger.Default.Send(new RefreshUnreadCountsMessage(category.MailAccountId));
+    }
+
+    public async Task<List<MailCategory>> GetCategoriesForMailAsync(Guid accountId, IEnumerable<Guid> mailCopyUniqueIds)
+    {
+        var uniqueIds = mailCopyUniqueIds?.Distinct().ToList() ?? [];
+        if (uniqueIds.Count == 0)
+            return [];
+
+        var placeholders = string.Join(",", uniqueIds.Select(_ => "?"));
+        var sql = $"SELECT DISTINCT MailCategory.* FROM {nameof(MailCategory)} " +
+                  $"INNER JOIN {nameof(MailCategoryAssignment)} ON {nameof(MailCategory)}.{nameof(MailCategory.Id)} = {nameof(MailCategoryAssignment)}.{nameof(MailCategoryAssignment.MailCategoryId)} " +
+                  $"WHERE {nameof(MailCategory)}.{nameof(MailCategory.MailAccountId)} = ? AND {nameof(MailCategoryAssignment)}.{nameof(MailCategoryAssignment.MailCopyUniqueId)} IN ({placeholders}) " +
+                  $"ORDER BY {nameof(MailCategory.Name)} COLLATE NOCASE";
+
+        return await Connection.QueryAsync<MailCategory>(
+            sql,
+            [accountId, .. uniqueIds.Cast<object>()]).ConfigureAwait(false);
+    }
+
+    public async Task<List<Guid>> GetAssignedCategoryIdsForAllAsync(IEnumerable<Guid> mailCopyUniqueIds)
+    {
+        var uniqueIds = mailCopyUniqueIds?.Distinct().ToList() ?? [];
+        if (uniqueIds.Count == 0)
+            return [];
+
+        var placeholders = string.Join(",", uniqueIds.Select(_ => "?"));
+        var sql = $"SELECT {nameof(MailCategoryAssignment.MailCategoryId)} " +
+                  $"FROM {nameof(MailCategoryAssignment)} " +
+                  $"WHERE {nameof(MailCategoryAssignment.MailCopyUniqueId)} IN ({placeholders}) " +
+                  $"GROUP BY {nameof(MailCategoryAssignment.MailCategoryId)} " +
+                  $"HAVING COUNT(DISTINCT {nameof(MailCategoryAssignment.MailCopyUniqueId)}) = ?";
+
+        return await Connection.QueryScalarsAsync<Guid>(
+            sql,
+            [.. uniqueIds.Cast<object>(), uniqueIds.Count]).ConfigureAwait(false);
+    }
+
+    public async Task<List<string>> GetCategoryNamesForMailAsync(Guid mailCopyUniqueId)
+    {
+        var sql = $"SELECT {nameof(MailCategory.Name)} " +
+                  $"FROM {nameof(MailCategory)} " +
+                  $"INNER JOIN {nameof(MailCategoryAssignment)} ON {nameof(MailCategory)}.{nameof(MailCategory.Id)} = {nameof(MailCategoryAssignment.MailCategoryId)} " +
+                  $"WHERE {nameof(MailCategoryAssignment.MailCopyUniqueId)} = ? " +
+                  $"ORDER BY {nameof(MailCategory.Name)} COLLATE NOCASE";
+
+        return await Connection.QueryScalarsAsync<string>(sql, mailCopyUniqueId).ConfigureAwait(false);
+    }
+
+    public async Task<List<MailCopy>> GetMailCopiesForCategoryAsync(Guid categoryId)
+    {
+        var sql = $"SELECT {nameof(MailCopy)}.* " +
+                  $"FROM {nameof(MailCopy)} " +
+                  $"INNER JOIN {nameof(MailCategoryAssignment)} ON {nameof(MailCopy)}.{nameof(MailCopy.UniqueId)} = {nameof(MailCategoryAssignment.MailCopyUniqueId)} " +
+                  $"WHERE {nameof(MailCategoryAssignment.MailCategoryId)} = ?";
+
+        return await Connection.QueryAsync<MailCopy>(sql, categoryId).ConfigureAwait(false);
+    }
+
+    public Task<List<UnreadCategoryCountResult>> GetUnreadCategoryCountResultsAsync(IEnumerable<Guid> accountIds)
+    {
+        var accountIdList = accountIds?.Distinct().ToList() ?? [];
+        if (accountIdList.Count == 0)
+            return Task.FromResult(new List<UnreadCategoryCountResult>());
+
+        var placeholders = string.Join(",", accountIdList.Select(_ => "?"));
+        var sql =
+            $"SELECT MailCategory.{nameof(MailCategory.Id)} as {nameof(UnreadCategoryCountResult.CategoryId)}, " +
+            $"MailCategory.{nameof(MailCategory.MailAccountId)} as {nameof(UnreadCategoryCountResult.AccountId)}, " +
+            $"COUNT(DISTINCT MailCopy.{nameof(MailCopy.UniqueId)}) as {nameof(UnreadCategoryCountResult.UnreadItemCount)} " +
+            $"FROM {nameof(MailCategory)} " +
+            $"INNER JOIN {nameof(MailCategoryAssignment)} ON {nameof(MailCategory)}.{nameof(MailCategory.Id)} = {nameof(MailCategoryAssignment)}.{nameof(MailCategoryAssignment.MailCategoryId)} " +
+            $"INNER JOIN {nameof(MailCopy)} ON {nameof(MailCategoryAssignment)}.{nameof(MailCategoryAssignment.MailCopyUniqueId)} = {nameof(MailCopy)}.{nameof(MailCopy.UniqueId)} " +
+            $"WHERE MailCategory.{nameof(MailCategory.MailAccountId)} IN ({placeholders}) AND MailCopy.{nameof(MailCopy.IsRead)} = 0 " +
+            $"GROUP BY MailCategory.{nameof(MailCategory.Id)}";
+
+        return Connection.QueryAsync<UnreadCategoryCountResult>(sql, accountIdList.Cast<object>().ToArray());
+    }
+
+    private void NotifyCategoryStructureChanged(Guid accountId)
+    {
+        WeakReferenceMessenger.Default.Send(new AccountsMenuRefreshRequested(false));
+        WeakReferenceMessenger.Default.Send(new RefreshUnreadCountsMessage(accountId));
+    }
+
+    private static string NormalizeCategoryName(string name)
+        => name?.Trim() ?? string.Empty;
+}

Wino.Services/MailService.cs

@@ -32,6 +32,7 @@ public class MailService : BaseDatabaseService, IMailService
     private readonly IMimeFileService _mimeFileService;
     private readonly IPreferencesService _preferencesService;
     private readonly ISentMailReceiptService _sentMailReceiptService;
+    private readonly IMailCategoryService _mailCategoryService;
 
     private readonly ILogger _logger = Log.ForContext<MailService>();
 
@@ -42,7 +43,8 @@ public class MailService : BaseDatabaseService, IMailService
                        ISignatureService signatureService,
                        IMimeFileService mimeFileService,
                        IPreferencesService preferencesService,
-                       ISentMailReceiptService sentMailReceiptService) : base(databaseService)
+                       ISentMailReceiptService sentMailReceiptService,
+                       IMailCategoryService mailCategoryService) : base(databaseService)
     {
         _folderService = folderService;
         _contactService = contactService;
@@ -51,6 +53,7 @@ public class MailService : BaseDatabaseService, IMailService
         _mimeFileService = mimeFileService;
         _preferencesService = preferencesService;
         _sentMailReceiptService = sentMailReceiptService;
+        _mailCategoryService = mailCategoryService;
     }
 
     public async Task<(MailCopy draftMailCopy, string draftBase64MimeMessage)> CreateDraftAsync(Guid accountId, DraftCreationOptions draftCreationOptions)
@@ -171,7 +174,9 @@ public class MailService : BaseDatabaseService, IMailService
     private static (string Query, object[] Parameters) BuildMailFetchQuery(MailListInitializationOptions options)
     {
         var sql = new StringBuilder();
-        sql.Append("SELECT MailCopy.* FROM MailCopy INNER JOIN MailItemFolder ON MailCopy.FolderId = MailItemFolder.Id");
+        sql.Append(options.IsCategoryView
+            ? "SELECT DISTINCT MailCopy.* FROM MailCopy INNER JOIN MailItemFolder ON MailCopy.FolderId = MailItemFolder.Id INNER JOIN MailCategoryAssignment ON MailCopy.UniqueId = MailCategoryAssignment.MailCopyUniqueId"
+            : "SELECT MailCopy.* FROM MailCopy INNER JOIN MailItemFolder ON MailCopy.FolderId = MailItemFolder.Id");
 
         var whereClauses = new List<string>();
         var parameters = new List<object>();
@@ -181,6 +186,13 @@ public class MailService : BaseDatabaseService, IMailService
         whereClauses.Add($"MailCopy.FolderId IN ({folderPlaceholders})");
         parameters.AddRange(options.Folders.Select(f => (object)f.Id));
 
+        if (options.IsCategoryView)
+        {
+            var categoryPlaceholders = string.Join(",", options.CategoryIds.Select(_ => "?"));
+            whereClauses.Add($"MailCategoryAssignment.MailCategoryId IN ({categoryPlaceholders})");
+            parameters.AddRange(options.CategoryIds.Select(a => (object)a));
+        }
+
         // Filter type
         switch (options.FilterType)
         {
@@ -338,7 +350,7 @@ public class MailService : BaseDatabaseService, IMailService
     {
         List<MailCopy> mails;
 
-        if (options.PreFetchMailCopies != null)
+        if (options.PreFetchMailCopies != null && !options.IsCategoryView)
         {
             mails = ApplyOptionsToPreFetchedMails(options);
         }
@@ -398,7 +410,7 @@ public class MailService : BaseDatabaseService, IMailService
         mails.RemoveAll(m => m.AssignedAccount == null || m.AssignedFolder == null);
         await _sentMailReceiptService.PopulateReceiptStatesAsync(mails).ConfigureAwait(false);
 
-        if (!options.CreateThreads || mails.Count == 0)
+        if (!options.CreateThreads || mails.Count == 0 || options.IsCategoryView)
             return [.. mails];
 
         // 6. Expand threads: one batch query for all sibling mails across all threads.
@@ -727,6 +739,7 @@ public class MailService : BaseDatabaseService, IMailService
         _logger.Debug("Deleting mail {Id} from folder {FolderName}", mailCopy.Id, mailCopy.AssignedFolder.FolderName);
 
         await Connection.DeleteAsync<MailCopy>(mailCopy.UniqueId).ConfigureAwait(false);
+        await Connection.ExecuteAsync("DELETE FROM MailCategoryAssignment WHERE MailCopyUniqueId = ?", mailCopy.UniqueId).ConfigureAwait(false);
 
         // If there are no more copies exists of the same mail, delete the MIME file as well.
         var isMailExists = await IsMailExistsAsync(mailCopy.Id).ConfigureAwait(false);
@@ -965,6 +978,7 @@ public class MailService : BaseDatabaseService, IMailService
             mailCopy.UniqueId = existingCopyItem.UniqueId;
 
             await UpdateMailAsync(mailCopy).ConfigureAwait(false);
+            await ReplaceMailCategoriesForPackageAsync(accountId, mailCopy, package).ConfigureAwait(false);
             await _sentMailReceiptService.TrackSentMailAsync(mailCopy, mimeMessage).ConfigureAwait(false);
             await _sentMailReceiptService.ProcessIncomingReceiptAsync(mailCopy, mimeMessage).ConfigureAwait(false);
 
@@ -981,6 +995,7 @@ public class MailService : BaseDatabaseService, IMailService
             }
 
             await InsertMailAsync(mailCopy).ConfigureAwait(false);
+            await ReplaceMailCategoriesForPackageAsync(accountId, mailCopy, package).ConfigureAwait(false);
             await _sentMailReceiptService.TrackSentMailAsync(mailCopy, mimeMessage).ConfigureAwait(false);
             await _sentMailReceiptService.ProcessIncomingReceiptAsync(mailCopy, mimeMessage).ConfigureAwait(false);
 
@@ -1017,6 +1032,11 @@ public class MailService : BaseDatabaseService, IMailService
         await _contactService.SaveAddressInformationAsync(contacts).ConfigureAwait(false);
     }
 
+    private Task ReplaceMailCategoriesForPackageAsync(Guid accountId, MailCopy mailCopy, NewMailItemPackage package)
+        => package?.CategoryNames == null
+            ? Task.CompletedTask
+            : _mailCategoryService.ReplaceMailAssignmentsAsync(accountId, mailCopy.UniqueId, package.CategoryNames);
+
     private async Task<MimeMessage> CreateDraftMimeAsync(MailAccount account, DraftCreationOptions draftCreationOptions, MailAccountAlias selectedAlias)
     {
         // This unique id is stored in mime headers for Wino to identify remote message with local copy.

Wino.Services/ServicesContainerSetup.cs

@@ -20,6 +20,7 @@ public static class ServicesContainerSetup
 
         services.AddTransient<ICalendarService, CalendarService>();
         services.AddTransient<IMailService, MailService>();
+        services.AddTransient<IMailCategoryService, MailCategoryService>();
         services.AddTransient<ISentMailReceiptService, SentMailReceiptService>();
         services.AddTransient<IFolderService, FolderService>();
         services.AddTransient<IAccountService, AccountService>();