diff --git a/Wino.Mail.WinUI/App.xaml.cs b/Wino.Mail.WinUI/App.xaml.cs
index a930ffe0..490d5c70 100644
--- a/Wino.Mail.WinUI/App.xaml.cs
+++ b/Wino.Mail.WinUI/App.xaml.cs
@@ -351,4 +351,29 @@ public partial class App : WinoApplication, IRecipient<NewMailSynchronizationReq
     {
         _synchronizationManager?.SynchronizeMailAsync(message.Options);
     }
+
+    /// <summary>
+    /// Handles activation redirected from another instance (single-instancing).
+    /// This is called when a second instance tries to launch and redirects to this existing instance.
+    /// </summary>
+    public void HandleRedirectedActivation(AppActivationArguments args)
+    {
+        // Dispatch to UI thread since this is called from Program.OnActivated
+        MainWindow?.DispatcherQueue.TryEnqueue(() =>
+        {
+            // Handle different activation kinds
+            if (args.Kind == ExtendedActivationKind.AppNotification)
+            {
+                // Handle toast notification activation
+                var toastArgs = (AppNotificationActivatedEventArgs)args.Data;
+                _ = HandleToastActivationAsync(toastArgs);
+            }
+            else
+            {
+                // For other activation types (Launch, Protocol, etc.), bring window to front
+                MainWindow?.BringToFront();
+                MainWindow?.Activate();
+            }
+        });
+    }
 }
diff --git a/Wino.Mail.WinUI/Program.cs b/Wino.Mail.WinUI/Program.cs
new file mode 100644
index 00000000..62d87af2
--- /dev/null
+++ b/Wino.Mail.WinUI/Program.cs
@@ -0,0 +1,104 @@
+using System;
+using System.Diagnostics;
+using System.Runtime.InteropServices;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.UI.Dispatching;
+using Microsoft.UI.Xaml;
+using Microsoft.Windows.AppLifecycle;
+
+namespace Wino.Mail.WinUI;
+
+public class Program
+{
+    [STAThread]
+    static int Main(string[] args)
+    {
+        WinRT.ComWrappersSupport.InitializeComWrappers();
+        bool isRedirect = DecideRedirection();
+
+        if (!isRedirect)
+        {
+            Application.Start((p) =>
+            {
+                var context = new DispatcherQueueSynchronizationContext(
+                    DispatcherQueue.GetForCurrentThread());
+                SynchronizationContext.SetSynchronizationContext(context);
+                _ = new App();
+            });
+        }
+
+        return 0;
+    }
+
+    private static bool DecideRedirection()
+    {
+        bool isRedirect = false;
+        AppActivationArguments args = AppInstance.GetCurrent().GetActivatedEventArgs();
+        ExtendedActivationKind kind = args.Kind;
+        AppInstance keyInstance = AppInstance.FindOrRegisterForKey("WinoMailSingleInstance");
+
+        if (keyInstance.IsCurrent)
+        {
+            keyInstance.Activated += OnActivated;
+        }
+        else
+        {
+            isRedirect = true;
+            RedirectActivationTo(args, keyInstance);
+        }
+
+        return isRedirect;
+    }
+
+    [DllImport("kernel32.dll", CharSet = CharSet.Unicode)]
+    private static extern IntPtr CreateEvent(
+        IntPtr lpEventAttributes, bool bManualReset,
+        bool bInitialState, string lpName);
+
+    [DllImport("kernel32.dll")]
+    private static extern bool SetEvent(IntPtr hEvent);
+
+    [DllImport("ole32.dll")]
+    private static extern uint CoWaitForMultipleObjects(
+        uint dwFlags, uint dwMilliseconds, ulong nHandles,
+        IntPtr[] pHandles, out uint dwIndex);
+
+    [DllImport("user32.dll")]
+    static extern bool SetForegroundWindow(IntPtr hWnd);
+
+    private static IntPtr redirectEventHandle = IntPtr.Zero;
+
+    // Do the redirection on another thread, and use a non-blocking
+    // wait method to wait for the redirection to complete.
+    public static void RedirectActivationTo(AppActivationArguments args,
+                                            AppInstance keyInstance)
+    {
+        redirectEventHandle = CreateEvent(IntPtr.Zero, true, false, null!);
+        Task.Run(() =>
+        {
+            keyInstance.RedirectActivationToAsync(args).AsTask().Wait();
+            SetEvent(redirectEventHandle);
+        });
+
+        uint CWMO_DEFAULT = 0;
+        uint INFINITE = 0xFFFFFFFF;
+        _ = CoWaitForMultipleObjects(
+           CWMO_DEFAULT, INFINITE, 1,
+           [redirectEventHandle], out uint handleIndex);
+
+        // Bring the window to the foreground
+        Process process = Process.GetProcessById((int)keyInstance.ProcessId);
+        SetForegroundWindow(process.MainWindowHandle);
+    }
+
+    private static void OnActivated(object? sender, AppActivationArguments args)
+    {
+        // When a new instance tries to launch, this event fires in the existing instance.
+        // We need to notify the App to handle the activation (e.g., bring window to front, handle protocol).
+        if (Application.Current is App app)
+        {
+            app.HandleRedirectedActivation(args);
+        }
+    }
+}
diff --git a/Wino.Mail.WinUI/Wino.Mail.WinUI.csproj b/Wino.Mail.WinUI/Wino.Mail.WinUI.csproj
index d27338d1..05a4576e 100644
--- a/Wino.Mail.WinUI/Wino.Mail.WinUI.csproj
+++ b/Wino.Mail.WinUI/Wino.Mail.WinUI.csproj
@@ -11,6 +11,7 @@
     <UseWinUI>true</UseWinUI>
     <EnableMsixTooling>true</EnableMsixTooling>
     <Nullable>enable</Nullable>
+    <DefineConstants>$(DefineConstants);DISABLE_XAML_GENERATED_MAIN</DefineConstants>
   </PropertyGroup>
   <ItemGroup>
     <Content Remove="Assets\BadgeLogo.scale-100.png" />