UI visuals for mail calendar items, calendar reminders.

Wino.Calendar.ViewModels/Data/CalendarItemViewModel.cs

@@ -4,6 +4,7 @@ using CommunityToolkit.Mvvm.ComponentModel;
 using Itenso.TimePeriod;
 using Wino.Core.Domain;
 using Wino.Core.Domain.Entities.Calendar;
+using Wino.Core.Domain.Extensions;
 using Wino.Core.Domain.Interfaces;
 using Wino.Core.Domain.Models.Calendar;
 
@@ -32,26 +33,8 @@ public partial class CalendarItemViewModel : ObservableObject, ICalendarItem, IC
         }
         set
         {
-            // When setting from UI (in local time), convert to event's timezone for storage
+            // When setting from UI (in local time), convert to event's timezone for storage.
-            if (!string.IsNullOrEmpty(CalendarItem.StartTimeZone))
+            CalendarItem.StartDate = value.ToTimeZoneFromLocal(CalendarItem.StartTimeZone);
-            {
-                try
-                {
-                    var sourceTimeZone = TimeZoneInfo.Local;
-                    var targetTimeZone = TimeZoneInfo.FindSystemTimeZoneById(CalendarItem.StartTimeZone);
-                    CalendarItem.StartDate = TimeZoneInfo.ConvertTime(value, sourceTimeZone, targetTimeZone);
-                }
-                catch
-                {
-                    // If timezone lookup fails, set as-is
-                    CalendarItem.StartDate = value;
-                }
-            }
-            else
-            {
-                // No timezone info, set as-is
-                CalendarItem.StartDate = value;
-            }
         }
     }
 

Wino.Core.Domain/Constants.cs

@@ -13,6 +13,9 @@ public static class Constants
     public const string ToastMailUniqueIdKey = nameof(ToastMailUniqueIdKey);
     public const string ToastActionKey = nameof(ToastActionKey);
     public const string ToastMailAccountIdKey = nameof(ToastMailAccountIdKey);
+    public const string ToastCalendarItemIdKey = nameof(ToastCalendarItemIdKey);
+    public const string ToastCalendarActionKey = nameof(ToastCalendarActionKey);
+    public const string ToastCalendarNavigateAction = nameof(ToastCalendarNavigateAction);
 
     public const string ClientLogFile = "Client_.log";
     public const string ServerLogFile = "Server_.log";

Wino.Core.Domain/Entities/Calendar/CalendarItem.cs

@@ -3,6 +3,7 @@ using System.Diagnostics;
 using Itenso.TimePeriod;
 using SQLite;
 using Wino.Core.Domain.Enums;
+using Wino.Core.Domain.Extensions;
 using Wino.Core.Domain.Interfaces;
 using Wino.Core.Domain.Models.Calendar;
 
@@ -168,28 +169,7 @@ public class CalendarItem : ICalendarItem
     {
         get
         {
-            if (string.IsNullOrEmpty(StartTimeZone))
+            return this.GetLocalStartDate();
-            {
-                // No timezone info, return as-is
-                return StartDate;
-            }
-
-            try
-            {
-                var sourceTimeZone = TimeZoneInfo.FindSystemTimeZoneById(StartTimeZone);
-                var localTimeZone = TimeZoneInfo.Local;
-
-                // Ensure DateTime is Unspecified kind before conversion
-                var unspecifiedDateTime = DateTime.SpecifyKind(StartDate, DateTimeKind.Unspecified);
-
-                // Convert from source timezone to local timezone
-                return TimeZoneInfo.ConvertTime(unspecifiedDateTime, sourceTimeZone, localTimeZone);
-            }
-            catch
-            {
-                // If timezone lookup fails, return as-is
-                return StartDate;
-            }
         }
     }
 
@@ -202,28 +182,7 @@ public class CalendarItem : ICalendarItem
     {
         get
         {
-            if (string.IsNullOrEmpty(EndTimeZone))
+            return this.GetLocalEndDate();
-            {
-                // No timezone info, return as-is
-                return EndDate;
-            }
-
-            try
-            {
-                var sourceTimeZone = TimeZoneInfo.FindSystemTimeZoneById(EndTimeZone);
-                var localTimeZone = TimeZoneInfo.Local;
-
-                // Ensure DateTime is Unspecified kind before conversion
-                var unspecifiedDateTime = DateTime.SpecifyKind(EndDate, DateTimeKind.Unspecified);
-
-                // Convert from source timezone to local timezone
-                return TimeZoneInfo.ConvertTime(unspecifiedDateTime, sourceTimeZone, localTimeZone);
-            }
-            catch
-            {
-                // If timezone lookup fails, return as-is
-                return EndDate;
-            }
         }
     }
 

Wino.Core.Domain/Extensions/DateTimeExtensions.cs

@@ -1,4 +1,5 @@
-using System;
+using System;
+using Wino.Core.Domain.Entities.Calendar;
 using Wino.Core.Domain.Models.Calendar;
 
 namespace Wino.Core.Domain.Extensions;
@@ -29,4 +30,56 @@ public static class DateTimeExtensions
         // Start loading from this date instead of visible date.
         return date.AddDays(-diff).Date;
     }
+
+    /// <summary>
+    /// Converts a datetime from source timezone into local timezone.
+    /// If timezone lookup fails, returns original value.
+    /// </summary>
+    public static DateTime ToLocalTimeFromTimeZone(this DateTime dateTime, string sourceTimeZoneId)
+    {
+        if (string.IsNullOrWhiteSpace(sourceTimeZoneId))
+            return dateTime;
+
+        try
+        {
+            var sourceTimeZone = TimeZoneInfo.FindSystemTimeZoneById(sourceTimeZoneId);
+            var localTimeZone = TimeZoneInfo.Local;
+            var unspecifiedDateTime = DateTime.SpecifyKind(dateTime, DateTimeKind.Unspecified);
+
+            return TimeZoneInfo.ConvertTime(unspecifiedDateTime, sourceTimeZone, localTimeZone);
+        }
+        catch
+        {
+            return dateTime;
+        }
+    }
+
+    /// <summary>
+    /// Converts local datetime into target timezone.
+    /// If timezone lookup fails, returns original value.
+    /// </summary>
+    public static DateTime ToTimeZoneFromLocal(this DateTime localDateTime, string targetTimeZoneId)
+    {
+        if (string.IsNullOrWhiteSpace(targetTimeZoneId))
+            return localDateTime;
+
+        try
+        {
+            var sourceTimeZone = TimeZoneInfo.Local;
+            var targetTimeZone = TimeZoneInfo.FindSystemTimeZoneById(targetTimeZoneId);
+            var unspecifiedDateTime = DateTime.SpecifyKind(localDateTime, DateTimeKind.Unspecified);
+
+            return TimeZoneInfo.ConvertTime(unspecifiedDateTime, sourceTimeZone, targetTimeZone);
+        }
+        catch
+        {
+            return localDateTime;
+        }
+    }
+
+    public static DateTime GetLocalStartDate(this CalendarItem calendarItem)
+        => calendarItem.StartDate.ToLocalTimeFromTimeZone(calendarItem.StartTimeZone);
+
+    public static DateTime GetLocalEndDate(this CalendarItem calendarItem)
+        => calendarItem.EndDate.ToLocalTimeFromTimeZone(calendarItem.EndTimeZone);
 }

Wino.Core.Domain/Interfaces/ICalendarService.cs

@@ -1,5 +1,6 @@
-using System;
+using System;
 using System.Collections.Generic;
+using System.Threading;
 using System.Threading.Tasks;
 using Itenso.TimePeriod;
 using Wino.Core.Domain.Entities.Calendar;
@@ -18,7 +19,7 @@ public interface ICalendarService
     Task InsertAccountCalendarAsync(AccountCalendar accountCalendar);
     Task UpdateAccountCalendarAsync(AccountCalendar accountCalendar);
     Task CreateNewCalendarItemAsync(CalendarItem calendarItem, List<CalendarEventAttendee> attendees);
-    
+
     /// <summary>
     /// Retrieves calendar events for a given calendar within the specified time period.
     /// </summary>
@@ -26,7 +27,7 @@ public interface ICalendarService
     /// <param name="period">The time period to query events for.</param>
     /// <returns>List of calendar items that fall within the requested period.</returns>
     Task<List<CalendarItem>> GetCalendarEventsAsync(IAccountCalendar calendar, ITimePeriod period);
-    
+
     Task<CalendarItem> GetCalendarItemAsync(Guid accountCalendarId, string remoteEventId);
     Task UpdateCalendarDeltaSynchronizationToken(Guid calendarId, string deltaToken);
 
@@ -42,6 +43,11 @@ public interface ICalendarService
     Task<List<Reminder>> GetRemindersAsync(Guid calendarItemId);
     Task SaveRemindersAsync(Guid calendarItemId, List<Reminder> reminders);
 
+    /// <summary>
+    /// Checks due reminder windows and returns reminder notifications that should trigger now.
+    /// </summary>
+    Task<List<CalendarReminderNotificationRequest>> CheckAndNotifyAsync(DateTime lastCheckLocal, DateTime nowLocal, ISet<string> sentReminderKeys, CancellationToken cancellationToken = default);
+
     /// <summary>
     /// Gets predefined reminder options in minutes (1 Hour, 30 Min, 15 Min, 5 Min, 1 Min).
     /// </summary>

Wino.Core.Domain/Interfaces/IMailItemDisplayInformation.cs

@@ -17,6 +17,7 @@ public interface IMailItemDisplayInformation : INotifyPropertyChanged
     bool IsRead { get; }
     bool IsDraft { get; }
     bool HasAttachments { get; }
+    bool IsCalendarEvent { get; }
     bool IsFlagged { get; }
     DateTime CreationDate { get; }
     string Base64ContactPicture { get; }

Wino.Core.Domain/Interfaces/INotificationBuilder.cs

@@ -1,6 +1,7 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
+using Wino.Core.Domain.Entities.Calendar;
 using Wino.Core.Domain.Entities.Mail;
 using Wino.Core.Domain.Entities.Shared;
 
@@ -29,4 +30,9 @@ public interface INotificationBuilder
     /// </summary>
     /// <param name="account">Account that needs attention.</param>
     void CreateAttentionRequiredNotification(MailAccount account);
+
+    /// <summary>
+    /// Creates a calendar reminder toast for the specified calendar item.
+    /// </summary>
+    Task CreateCalendarReminderNotificationAsync(CalendarItem calendarItem, long reminderDurationInSeconds);
 }

Wino.Core.Domain/Models/Calendar/CalendarReminderNotificationRequest.cs

@@ -0,0 +1,10 @@
+using Wino.Core.Domain.Entities.Calendar;
+
+namespace Wino.Core.Domain.Models.Calendar;
+
+public sealed class CalendarReminderNotificationRequest
+{
+    public CalendarItem CalendarItem { get; init; } = null!;
+    public long ReminderDurationInSeconds { get; init; }
+    public string ReminderKey { get; init; } = string.Empty;
+}

Wino.Core.Tests/Services/CalendarReminderServiceTests.cs

@@ -0,0 +1,227 @@
+using FluentAssertions;
+using Wino.Core.Domain.Entities.Calendar;
+using Wino.Core.Domain.Entities.Shared;
+using Wino.Core.Domain.Enums;
+using Wino.Core.Tests.Helpers;
+using Wino.Services;
+using Xunit;
+
+namespace Wino.Core.Tests.Services;
+
+public class CalendarReminderServiceTests : IAsyncLifetime
+{
+    private InMemoryDatabaseService _databaseService = null!;
+    private CalendarService _calendarService = null!;
+    private AccountCalendar _testCalendar = null!;
+
+    public async Task InitializeAsync()
+    {
+        _databaseService = new InMemoryDatabaseService();
+        await _databaseService.InitializeAsync();
+        _calendarService = new CalendarService(_databaseService);
+
+        var account = new MailAccount
+        {
+            Id = Guid.NewGuid(),
+            Name = "Reminder Test",
+            Address = "reminder@test.local",
+            SenderName = "Reminder Test",
+            IsCalendarAccessGranted = true
+        };
+
+        await _databaseService.Connection.InsertAsync(account, typeof(MailAccount));
+
+        _testCalendar = new AccountCalendar
+        {
+            Id = Guid.NewGuid(),
+            AccountId = account.Id,
+            Name = "Test Calendar",
+            TimeZone = "UTC",
+            IsPrimary = true,
+            BackgroundColorHex = "#0A84FF",
+            TextColorHex = "#FFFFFF"
+        };
+
+        await _calendarService.InsertAccountCalendarAsync(_testCalendar);
+    }
+
+    public async Task DisposeAsync()
+    {
+        await _databaseService.DisposeAsync();
+    }
+
+    [Fact]
+    public async Task CheckAndNotifyAsync_WhenReminderFallsWithinWindow_ReturnsDueReminder()
+    {
+        var nowLocal = new DateTime(2026, 1, 1, 10, 0, 0);
+        var lastCheckLocal = nowLocal.AddSeconds(-30);
+
+        var calendarItem = await CreateCalendarItemWithReminderAsync(
+            startDate: nowLocal.AddMinutes(5),
+            reminderDurationInSeconds: 5 * 60,
+            reminderType: CalendarItemReminderType.Popup);
+
+        HashSet<string> sentReminderKeys = [];
+
+        var due = await _calendarService.CheckAndNotifyAsync(lastCheckLocal, nowLocal, sentReminderKeys);
+
+        due.Should().HaveCount(1);
+        due[0].CalendarItem.Id.Should().Be(calendarItem.Id);
+        due[0].ReminderDurationInSeconds.Should().Be(5 * 60);
+        due[0].ReminderKey.Should().Be($"{calendarItem.Id:N}:{5 * 60}");
+        sentReminderKeys.Should().Contain($"{calendarItem.Id:N}:{5 * 60}");
+    }
+
+    [Fact]
+    public async Task CheckAndNotifyAsync_WhenReminderIsOutsideWindow_ReturnsEmpty()
+    {
+        var nowLocal = new DateTime(2026, 1, 1, 10, 0, 0);
+        var lastCheckLocal = nowLocal.AddSeconds(-30);
+
+        await CreateCalendarItemWithReminderAsync(
+            startDate: nowLocal.AddMinutes(20),
+            reminderDurationInSeconds: 5 * 60,
+            reminderType: CalendarItemReminderType.Popup);
+
+        HashSet<string> sentReminderKeys = [];
+
+        var due = await _calendarService.CheckAndNotifyAsync(lastCheckLocal, nowLocal, sentReminderKeys);
+
+        due.Should().BeEmpty();
+    }
+
+    [Fact]
+    public async Task CheckAndNotifyAsync_WhenReminderAlreadySent_DoesNotReturnDuplicate()
+    {
+        var nowLocal = new DateTime(2026, 1, 1, 10, 0, 0);
+        var lastCheckLocal = nowLocal.AddSeconds(-30);
+
+        var calendarItem = await CreateCalendarItemWithReminderAsync(
+            startDate: nowLocal.AddMinutes(5),
+            reminderDurationInSeconds: 5 * 60,
+            reminderType: CalendarItemReminderType.Popup);
+
+        HashSet<string> sentReminderKeys = [];
+
+        var firstRun = await _calendarService.CheckAndNotifyAsync(lastCheckLocal, nowLocal, sentReminderKeys);
+        var secondRun = await _calendarService.CheckAndNotifyAsync(lastCheckLocal, nowLocal, sentReminderKeys);
+
+        firstRun.Should().HaveCount(1);
+        secondRun.Should().BeEmpty();
+        sentReminderKeys.Should().Contain($"{calendarItem.Id:N}:{5 * 60}");
+    }
+
+    [Fact]
+    public async Task CheckAndNotifyAsync_WhenCalendarAccessNotGranted_ReturnsEmpty()
+    {
+        var restrictedAccount = new MailAccount
+        {
+            Id = Guid.NewGuid(),
+            Name = "No Calendar Access",
+            Address = "restricted@test.local",
+            SenderName = "Restricted",
+            IsCalendarAccessGranted = false
+        };
+        await _databaseService.Connection.InsertAsync(restrictedAccount, typeof(MailAccount));
+
+        var restrictedCalendar = new AccountCalendar
+        {
+            Id = Guid.NewGuid(),
+            AccountId = restrictedAccount.Id,
+            Name = "Restricted Calendar",
+            TimeZone = "UTC",
+            IsPrimary = true,
+            BackgroundColorHex = "#111111",
+            TextColorHex = "#FFFFFF"
+        };
+        await _calendarService.InsertAccountCalendarAsync(restrictedCalendar);
+
+        var nowLocal = new DateTime(2026, 1, 1, 10, 0, 0);
+        var lastCheckLocal = nowLocal.AddSeconds(-30);
+
+        await CreateCalendarItemWithReminderAsync(
+            startDate: nowLocal.AddMinutes(5),
+            reminderDurationInSeconds: 5 * 60,
+            reminderType: CalendarItemReminderType.Popup,
+            calendarId: restrictedCalendar.Id);
+
+        HashSet<string> sentReminderKeys = [];
+
+        var due = await _calendarService.CheckAndNotifyAsync(lastCheckLocal, nowLocal, sentReminderKeys);
+
+        due.Should().BeEmpty();
+    }
+
+    [Fact]
+    public async Task CheckAndNotifyAsync_WhenReminderTypeIsEmail_ReturnsEmpty()
+    {
+        var nowLocal = new DateTime(2026, 1, 1, 10, 0, 0);
+        var lastCheckLocal = nowLocal.AddSeconds(-30);
+
+        await CreateCalendarItemWithReminderAsync(
+            startDate: nowLocal.AddMinutes(5),
+            reminderDurationInSeconds: 5 * 60,
+            reminderType: CalendarItemReminderType.Email);
+
+        HashSet<string> sentReminderKeys = [];
+
+        var due = await _calendarService.CheckAndNotifyAsync(lastCheckLocal, nowLocal, sentReminderKeys);
+
+        due.Should().BeEmpty();
+    }
+
+    [Fact]
+    public async Task CheckAndNotifyAsync_WhenItemIsRecurringParent_ReturnsEmpty()
+    {
+        var nowLocal = new DateTime(2026, 1, 1, 10, 0, 0);
+        var lastCheckLocal = nowLocal.AddSeconds(-30);
+
+        await CreateCalendarItemWithReminderAsync(
+            startDate: nowLocal.AddMinutes(5),
+            reminderDurationInSeconds: 5 * 60,
+            reminderType: CalendarItemReminderType.Popup,
+            recurrence: "RRULE:FREQ=DAILY;COUNT=5");
+
+        HashSet<string> sentReminderKeys = [];
+
+        var due = await _calendarService.CheckAndNotifyAsync(lastCheckLocal, nowLocal, sentReminderKeys);
+
+        due.Should().BeEmpty();
+    }
+
+    private async Task<CalendarItem> CreateCalendarItemWithReminderAsync(
+        DateTime startDate,
+        long reminderDurationInSeconds,
+        CalendarItemReminderType reminderType,
+        Guid? calendarId = null,
+        string? recurrence = null)
+    {
+        var item = new CalendarItem
+        {
+            Id = Guid.NewGuid(),
+            Title = "Reminder Test Event",
+            StartDate = startDate,
+            StartTimeZone = string.Empty,
+            EndTimeZone = string.Empty,
+            DurationInSeconds = 60 * 30,
+            CalendarId = calendarId ?? _testCalendar.Id,
+            IsHidden = false,
+            Recurrence = recurrence ?? string.Empty
+        };
+
+        await _calendarService.CreateNewCalendarItemAsync(item, null);
+
+        await _calendarService.SaveRemindersAsync(item.Id,
+        [
+            new Reminder
+            {
+                Id = Guid.NewGuid(),
+                CalendarItemId = item.Id,
+                DurationInSeconds = reminderDurationInSeconds,
+                ReminderType = reminderType
+            }
+        ]);
+
+        return item;
+    }
+}

Wino.Core.ViewModels/PersonalizationPageViewModel.cs

@@ -338,6 +338,7 @@ public partial class PersonalizationPageViewModel : CoreBaseViewModel
         public bool IsRead { get; } = false;
         public bool IsDraft { get; } = false;
         public bool HasAttachments { get; } = false;
+        public bool IsCalendarEvent { get; } = false;
         public bool IsFlagged { get; } = false;
         public DateTime CreationDate { get; } = DateTime.Now;
         public string Base64ContactPicture { get; } = string.Empty;

Wino.Mail.ViewModels/Data/MailItemViewModel.cs

@@ -26,6 +26,7 @@ public partial class MailItemViewModel(MailCopy mailCopy) : ObservableRecipient,
     [NotifyPropertyChangedFor(nameof(PreviewText))]
     [NotifyPropertyChangedFor(nameof(FromAddress))]
     [NotifyPropertyChangedFor(nameof(HasAttachments))]
+    [NotifyPropertyChangedFor(nameof(IsCalendarEvent))]
     [NotifyPropertyChangedFor(nameof(Importance))]
     [NotifyPropertyChangedFor(nameof(ThreadId))]
     [NotifyPropertyChangedFor(nameof(MessageId))]
@@ -140,6 +141,8 @@ public partial class MailItemViewModel(MailCopy mailCopy) : ObservableRecipient,
         set => SetProperty(MailCopy.HasAttachments, value, MailCopy, (u, n) => u.HasAttachments = n);
     }
 
+    public bool IsCalendarEvent => MailCopy.ItemType == MailItemType.CalendarInvitation;
+
     public MailImportance Importance
     {
         get => MailCopy.Importance;
@@ -258,6 +261,7 @@ public partial class MailItemViewModel(MailCopy mailCopy) : ObservableRecipient,
         OnPropertyChanged(nameof(PreviewText));
         OnPropertyChanged(nameof(FromAddress));
         OnPropertyChanged(nameof(HasAttachments));
+        OnPropertyChanged(nameof(IsCalendarEvent));
         OnPropertyChanged(nameof(Importance));
         OnPropertyChanged(nameof(ThreadId));
         OnPropertyChanged(nameof(MessageId));

Wino.Mail.ViewModels/Data/ThreadMailItemViewModel.cs

@@ -79,6 +79,11 @@ public partial class ThreadMailItemViewModel : ObservableRecipient, IMailListIte
     /// </summary>
     public bool HasAttachments => ThreadEmails.Any(e => e.HasAttachments);
 
+    /// <summary>
+    /// Gets whether any email in this thread is a calendar invitation.
+    /// </summary>
+    public bool IsCalendarEvent => ThreadEmails.Any(e => e.IsCalendarEvent);
+
     /// <summary>
     /// Gets whether any email in this thread is flagged
     /// </summary>
@@ -167,6 +172,7 @@ public partial class ThreadMailItemViewModel : ObservableRecipient, IMailListIte
     [NotifyPropertyChangedFor(nameof(FromAddress))]
     [NotifyPropertyChangedFor(nameof(PreviewText))]
     [NotifyPropertyChangedFor(nameof(HasAttachments))]
+    [NotifyPropertyChangedFor(nameof(IsCalendarEvent))]
     [NotifyPropertyChangedFor(nameof(IsFlagged))]
     [NotifyPropertyChangedFor(nameof(IsFocused))]
     [NotifyPropertyChangedFor(nameof(IsRead))]
@@ -275,6 +281,7 @@ public partial class ThreadMailItemViewModel : ObservableRecipient, IMailListIte
         OnPropertyChanged(nameof(FromAddress));
         OnPropertyChanged(nameof(PreviewText));
         OnPropertyChanged(nameof(HasAttachments));
+        OnPropertyChanged(nameof(IsCalendarEvent));
         OnPropertyChanged(nameof(IsFlagged));
         OnPropertyChanged(nameof(IsFocused));
         OnPropertyChanged(nameof(IsRead));

Wino.Mail.WinUI/App.xaml.cs

@@ -15,6 +15,7 @@ using Wino.Core;
 using Wino.Core.Domain;
 using Wino.Core.Domain.Enums;
 using Wino.Core.Domain.Interfaces;
+using Wino.Core.Domain.Models.Calendar;
 using Wino.Core.Domain.Models.MailItem;
 using Wino.Core.Domain.Models.Synchronization;
 using Wino.Mail.Services;
@@ -179,6 +180,16 @@ public partial class App : WinoApplication,
     {
         var toastArguments = ToastArguments.Parse(toastArgs.Argument);
 
+        // Check calendar reminder toast activation first.
+        if (toastArguments.TryGetValue(Constants.ToastCalendarActionKey, out string calendarAction) &&
+            calendarAction == Constants.ToastCalendarNavigateAction &&
+            toastArguments.TryGetValue(Constants.ToastCalendarItemIdKey, out string calendarItemIdString) &&
+            Guid.TryParse(calendarItemIdString, out Guid calendarItemId))
+        {
+            await HandleCalendarToastNavigationAsync(calendarItemId);
+            return;
+        }
+
         // Check if this is a navigation toast (user clicked the notification).
         if (toastArguments.TryGetValue(Constants.ToastActionKey, out MailOperation action) &&
             Guid.TryParse(toastArguments[Constants.ToastMailUniqueIdKey], out Guid mailItemUniqueId))
@@ -198,6 +209,31 @@ public partial class App : WinoApplication,
         }
     }
 
+    private async Task HandleCalendarToastNavigationAsync(Guid calendarItemId)
+    {
+        var calendarService = Services.GetRequiredService<ICalendarService>();
+        var navigationService = Services.GetRequiredService<INavigationService>();
+
+        var calendarItem = await calendarService.GetCalendarItemAsync(calendarItemId).ConfigureAwait(false);
+        if (calendarItem == null)
+            return;
+
+        var target = new CalendarItemTarget(calendarItem, CalendarEventTargetType.Single);
+
+        if (!IsAppRunning())
+        {
+            await CreateAndActivateWindow(null!);
+        }
+        else
+        {
+            MainWindow.BringToFront();
+            MainWindow.Activate();
+        }
+
+        navigationService.ChangeApplicationMode(Core.Domain.Enums.WinoApplicationMode.Calendar);
+        navigationService.Navigate(WinoPage.EventDetailsPage, target);
+    }
+
     /// <summary>
     /// Handles toast notification click for navigation.
     /// Creates window if not running, sets up navigation parameter.

Wino.Mail.WinUI/Controls/CalendarMailItemDisplayInformationControl.xaml

@@ -7,7 +7,6 @@
     xmlns:helpers="using:Wino.Helpers"
     HorizontalAlignment="Stretch"
     VerticalAlignment="Stretch">
-
     <Grid x:DefaultBindMode="OneWay">
         <Grid.RowDefinitions>
             <RowDefinition Height="Auto" />
@@ -23,14 +22,30 @@
             Prefer24HourTimeFormat="{x:Bind Prefer24HourTimeFormat, Mode=OneWay}"
             ShowPreviewText="False" />
 
-        <TextBlock
+        <Grid
-            x:Name="EventDateText"
+            x:Name="EventDateContainer"
             Grid.Row="1"
-            Margin="53,0,12,8"
+            Margin="46,0,12,8">
-            FontSize="12"
+            <Grid.ColumnDefinitions>
-            Opacity="0.75"
+                <ColumnDefinition Width="Auto" />
-            Text="{x:Bind EventDateRangeText, Mode=OneWay}"
+                <ColumnDefinition Width="*" />
-            TextTrimming="CharacterEllipsis" />
+            </Grid.ColumnDefinitions>
+            <ContentPresenter
+                x:Name="CalendarInvitationContent"
+                Grid.Column="0"
+                Margin="0,0,4,0"
+                VerticalAlignment="Center"
+                x:Load="{x:Bind MailItem.IsCalendarEvent, Mode=OneWay}"
+                ContentTemplate="{StaticResource CalendarInvitationSymbolControlTemplate}" />
+            <TextBlock
+                x:Name="EventDateText"
+                Grid.Column="1"
+                Margin="4,0,2,0"
+                FontSize="12"
+                Opacity="0.75"
+                Text="{x:Bind EventDateRangeText, Mode=OneWay}"
+                TextTrimming="CharacterEllipsis" />
+        </Grid>
     </Grid>
 
     <VisualStateManager.VisualStateGroups>

Wino.Mail.WinUI/CoreUWPContainerSetup.cs

@@ -3,6 +3,7 @@ using Microsoft.UI.Xaml;
 using Wino.Core.Domain.Interfaces;
 using Wino.Core.ViewModels;
 using Wino.Core.WinUI.Services;
+using Wino.Mail.WinUI.Interfaces;
 using Wino.Mail.WinUI.Services;
 using Wino.Services;
 
@@ -29,6 +30,7 @@ public static class CoreUWPContainerSetup
         services.AddTransient<IStoreRatingService, StoreRatingService>();
         services.AddTransient<IKeyPressService, KeyPressService>();
         services.AddTransient<INotificationBuilder, NotificationBuilder>();
+        services.AddSingleton<ICalendarReminderServer, CalendarReminderServer>();
         services.AddTransient<IClipboardService, ClipboardService>();
         services.AddTransient<IStartupBehaviorService, StartupBehaviorService>();
         services.AddSingleton<IPrintService, PrintService>();

Wino.Mail.WinUI/Interfaces/ICalendarReminderServer.cs

@@ -0,0 +1,8 @@
+using System.Threading.Tasks;
+
+namespace Wino.Mail.WinUI.Interfaces;
+
+public interface ICalendarReminderServer
+{
+    Task StartAsync();
+}

Wino.Mail.WinUI/Services/CalendarReminderServer.cs

@@ -0,0 +1,107 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Serilog;
+using Wino.Core.Domain.Interfaces;
+using Wino.Mail.WinUI.Interfaces;
+
+namespace Wino.Mail.WinUI.Services;
+
+public class CalendarReminderServer : ICalendarReminderServer
+{
+    private static readonly TimeSpan PollingInterval = TimeSpan.FromSeconds(30);
+
+    private readonly ICalendarService _calendarService;
+    private readonly IAccountService _accountService;
+    private readonly INotificationBuilder _notificationBuilder;
+    private readonly ILogger _logger = Log.ForContext<CalendarReminderServer>();
+    private readonly SemaphoreSlim _startLock = new(1, 1);
+    private readonly HashSet<string> _sentReminderKeys = [];
+
+    private Task? _loopTask;
+    private CancellationTokenSource? _loopCts;
+    private DateTime _lastCheckLocal = DateTime.MinValue;
+
+    public CalendarReminderServer(ICalendarService calendarService, IAccountService accountService, INotificationBuilder notificationBuilder)
+    {
+        _calendarService = calendarService;
+        _accountService = accountService;
+        _notificationBuilder = notificationBuilder;
+    }
+
+    public async Task StartAsync()
+    {
+        await _startLock.WaitAsync().ConfigureAwait(false);
+
+        try
+        {
+            if (_loopTask != null)
+                return;
+
+            var accounts = await _accountService.GetAccountsAsync().ConfigureAwait(false);
+
+            var hasCalendarAccess = accounts.Exists(a => a.IsCalendarAccessGranted);
+
+            if (!hasCalendarAccess)
+            {
+                _logger.Information("Calendar reminder server will not start because no account has calendar access.");
+                return;
+            }
+
+            _lastCheckLocal = DateTime.Now.AddSeconds(-30);
+            _loopCts = new CancellationTokenSource();
+            _loopTask = RunLoopAsync(_loopCts.Token);
+
+            _logger.Information("Calendar reminder server started.");
+        }
+        finally
+        {
+            _startLock.Release();
+        }
+    }
+
+    private async Task RunLoopAsync(CancellationToken cancellationToken)
+    {
+        using var timer = new PeriodicTimer(PollingInterval);
+
+        try
+        {
+            while (await timer.WaitForNextTickAsync(cancellationToken).ConfigureAwait(false))
+            {
+                await ExecuteTickAsync(cancellationToken).ConfigureAwait(false);
+            }
+        }
+        catch (OperationCanceledException)
+        {
+            // no-op
+        }
+        catch (Exception ex)
+        {
+            _logger.Error(ex, "Calendar reminder server loop terminated unexpectedly.");
+        }
+    }
+
+    private async Task ExecuteTickAsync(CancellationToken cancellationToken)
+    {
+        var nowLocal = DateTime.Now;
+
+        if (_lastCheckLocal == DateTime.MinValue)
+            _lastCheckLocal = nowLocal.AddSeconds(-PollingInterval.TotalSeconds);
+
+        var dueNotifications = await _calendarService
+            .CheckAndNotifyAsync(_lastCheckLocal, nowLocal, _sentReminderKeys, cancellationToken)
+            .ConfigureAwait(false);
+
+        foreach (var reminder in dueNotifications)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+
+            await _notificationBuilder
+                .CreateCalendarReminderNotificationAsync(reminder.CalendarItem, reminder.ReminderDurationInSeconds)
+                .ConfigureAwait(false);
+        }
+
+        _lastCheckLocal = nowLocal;
+    }
+}

Wino.Mail.WinUI/Services/NotificationBuilder.cs

@@ -7,6 +7,7 @@ using Microsoft.Toolkit.Uwp.Notifications;
 using Serilog;
 using Windows.Data.Xml.Dom;
 using Windows.UI.Notifications;
+using Wino.Core.Domain.Entities.Calendar;
 using Wino.Core.Domain;
 using Wino.Core.Domain.Entities.Mail;
 using Wino.Core.Domain.Entities.Shared;
@@ -250,4 +251,38 @@ public class NotificationBuilder : INotificationBuilder
         builder.AddButton(new ToastButton().SetContent(Translator.Buttons_FixAccount));
         builder.Show();
     }
+
+    public Task CreateCalendarReminderNotificationAsync(CalendarItem calendarItem, long reminderDurationInSeconds)
+    {
+        if (calendarItem == null)
+            return Task.CompletedTask;
+
+        var builder = new ToastContentBuilder();
+        builder.SetToastScenario(ToastScenario.Reminder);
+
+        var localStart = calendarItem.LocalStartDate;
+        var reminderMinutes = (int)Math.Max(0, reminderDurationInSeconds / 60);
+        var reminderContext = reminderMinutes > 0
+            ? $"Starts in {reminderMinutes} minute{(reminderMinutes == 1 ? string.Empty : "s")}"
+            : "Starting now";
+
+        builder.AddText(calendarItem.Title);
+        builder.AddText($"{reminderContext} - {localStart:g}");
+
+        if (!string.IsNullOrWhiteSpace(calendarItem.Location))
+            builder.AddText(calendarItem.Location);
+
+        builder.AddArgument(Constants.ToastCalendarActionKey, Constants.ToastCalendarNavigateAction);
+        builder.AddArgument(Constants.ToastCalendarItemIdKey, calendarItem.Id.ToString());
+        builder.AddButton(GetDismissButton());
+        builder.AddAudio(new ToastAudio()
+        {
+            Src = new Uri("ms-winsoundevent:Notification.Reminder")
+        });
+
+        var tag = $"calendar-reminder-{calendarItem.Id:N}-{reminderDurationInSeconds}";
+        builder.Show(toast => toast.Tag = tag);
+
+        return Task.CompletedTask;
+    }
 }

Wino.Mail.WinUI/ShellWindow.xaml.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.ObjectModel;
 using System.Linq;
+using System.Threading.Tasks;
 using System.Windows.Input;
 using CommunityToolkit.Mvvm.Input;
 using CommunityToolkit.Mvvm.Messaging;
@@ -34,6 +35,7 @@ public sealed partial class ShellWindow : WindowEx, IWinoShellWindow,
     public ICommand ExitWinoCommand { get; set; }
 
     public ObservableCollection<SynchronizationActionItem> SyncActionItems { get; } = new();
+    private bool _calendarReminderServerStartAttempted;
 
     public ShellWindow()
     {
@@ -155,6 +157,12 @@ public sealed partial class ShellWindow : WindowEx, IWinoShellWindow,
 
     private void MainFrameNavigated(object sender, Microsoft.UI.Xaml.Navigation.NavigationEventArgs e)
     {
+        if (!_calendarReminderServerStartAttempted)
+        {
+            _calendarReminderServerStartAttempted = true;
+            _ = StartCalendarReminderServerAsync();
+        }
+
         // Mail shell has shell content only for mail list page
         // Thus, we check if the current content is MailAppShell
 
@@ -164,6 +172,23 @@ public sealed partial class ShellWindow : WindowEx, IWinoShellWindow,
             ShellTitleBar.Content = basePage.ShellContent;
     }
 
+    private async Task StartCalendarReminderServerAsync()
+    {
+        try
+        {
+            var reminderServer = WinoApplication.Current.Services.GetService<ICalendarReminderServer>();
+            if (reminderServer != null)
+            {
+                await reminderServer.StartAsync();
+            }
+        }
+        catch (Exception ex)
+        {
+            _calendarReminderServerStartAttempted = false;
+            Serilog.Log.Error(ex, "Failed to start calendar reminder server.");
+        }
+    }
+
     private void PaneButtonClicked(Microsoft.UI.Xaml.Controls.TitleBar sender, object args)
     {
         PreferencesService.IsNavigationPaneOpened = !PreferencesService.IsNavigationPaneOpened;

Wino.Mail.WinUI/Styles/ContentPresenters.xaml

@@ -29,4 +29,14 @@
                 Icon="Attachment" />
         </Viewbox>
     </DataTemplate>
+
+    <!--  Calendar invitation  -->
+    <DataTemplate x:Key="CalendarInvitationSymbolControlTemplate">
+        <Viewbox
+            Width="14"
+            HorizontalAlignment="Center"
+            VerticalAlignment="Bottom">
+            <controls:WinoFontIcon Margin="2,0,0,0" Icon="Calendar" />
+        </Viewbox>
+    </DataTemplate>
 </ResourceDictionary>

Wino.Services/CalendarService.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 using CommunityToolkit.Mvvm.Messaging;
 using Itenso.TimePeriod;
@@ -9,6 +10,7 @@ using Serilog;
 using Wino.Core.Domain.Entities.Calendar;
 using Wino.Core.Domain.Entities.Shared;
 using Wino.Core.Domain.Enums;
+using Wino.Core.Domain.Extensions;
 using Wino.Core.Domain.Interfaces;
 using Wino.Core.Domain.Models.Calendar;
 using Wino.Messaging.Client.Calendar;
@@ -332,6 +334,60 @@ public class CalendarService : BaseDatabaseService, ICalendarService
         });
     }
 
+    public async Task<List<CalendarReminderNotificationRequest>> CheckAndNotifyAsync(DateTime lastCheckLocal, DateTime nowLocal, ISet<string> sentReminderKeys, CancellationToken cancellationToken = default)
+    {
+        if (sentReminderKeys == null)
+            return [];
+
+        var candidates = await Connection.QueryAsync<CalendarReminderCandidate>(
+            @"
+            SELECT
+                c.Id AS CalendarItemId,
+                c.StartDate,
+                c.StartTimeZone,
+                r.DurationInSeconds AS ReminderDurationInSeconds
+            FROM CalendarItem c
+            INNER JOIN Reminder r ON r.CalendarItemId = c.Id
+            INNER JOIN AccountCalendar ac ON ac.Id = c.CalendarId
+            INNER JOIN MailAccount ma ON ma.Id = ac.AccountId
+            WHERE
+                c.IsHidden = 0
+                AND ma.IsCalendarAccessGranted = 1
+                AND r.ReminderType = 0
+                AND NOT (IFNULL(c.Recurrence, '') != '' AND c.RecurringCalendarItemId IS NULL)")
+            .ConfigureAwait(false);
+
+        var dueNotifications = new List<CalendarReminderNotificationRequest>();
+
+        foreach (var candidate in candidates)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+
+            var eventStartLocal = candidate.StartDate.ToLocalTimeFromTimeZone(candidate.StartTimeZone);
+            var triggerTimeLocal = eventStartLocal.AddSeconds(-candidate.ReminderDurationInSeconds);
+
+            if (triggerTimeLocal <= lastCheckLocal || triggerTimeLocal > nowLocal)
+                continue;
+
+            var reminderKey = $"{candidate.CalendarItemId:N}:{candidate.ReminderDurationInSeconds}";
+            if (!sentReminderKeys.Add(reminderKey))
+                continue;
+
+            var calendarItem = await GetCalendarItemAsync(candidate.CalendarItemId).ConfigureAwait(false);
+            if (calendarItem == null)
+                continue;
+
+            dueNotifications.Add(new CalendarReminderNotificationRequest()
+            {
+                CalendarItem = calendarItem,
+                ReminderDurationInSeconds = candidate.ReminderDurationInSeconds,
+                ReminderKey = reminderKey
+            });
+        }
+
+        return dueNotifications;
+    }
+
     #region Attachments
 
     public Task<List<CalendarAttachment>> GetAttachmentsAsync(Guid calendarItemId)
@@ -379,4 +435,12 @@ public class CalendarService : BaseDatabaseService, ICalendarService
     }
 
     #endregion
+
+    private sealed class CalendarReminderCandidate
+    {
+        public Guid CalendarItemId { get; set; }
+        public DateTime StartDate { get; set; }
+        public string StartTimeZone { get; set; }
+        public long ReminderDurationInSeconds { get; set; }
+    }
 }