Some threading stuff.

Wino.Core/Extensions/OutlookIntegratorExtensions.cs

@@ -69,7 +69,7 @@ public static class OutlookIntegratorExtensions
         return mailCopy;
     }
 
-    public static Message AsOutlookMessage(this MimeMessage mime, bool includeInternetHeaders)
+    public static Message AsOutlookMessage(this MimeMessage mime, bool includeInternetHeaders, string conversationId = null)
     {
         var fromAddress = GetRecipients(mime.From).ElementAt(0);
         var toAddresses = GetRecipients(mime.To).ToList();
@@ -93,6 +93,12 @@ public static class OutlookIntegratorExtensions
             Attachments = []
         };
 
+        // Set ConversationId if provided to maintain threading
+        if (!string.IsNullOrEmpty(conversationId))
+        {
+            message.ConversationId = conversationId;
+        }
+
         // Headers are only included when creating the draft.
         // When sending, they are not included. Graph will throw an error.
 

Wino.Core/Synchronizers/OutlookSynchronizer.cs

@@ -1231,7 +1231,9 @@ public class OutlookSynchronizer : WinoSynchronizer<RequestInformation, Message,
         // Alias support is lacking with direct MIMEs.
         // Therefore we convert the MIME message to Outlook message and use proper APIs.
 
-        var outlookMessage = mimeMessage.AsOutlookMessage(false);
+        // Pass the ConversationId (ThreadId) to maintain threading for replies/forwards
+        var conversationId = sendDraftPreparationRequest.MailItem.ThreadId;
+        var outlookMessage = mimeMessage.AsOutlookMessage(false, conversationId);
 
         // Create attachment requests.
         // TODO: We need to support large file attachments with sessioned upload at some point.

Wino.Mail.ViewModels/Collections/WinoMailCollection.cs

@@ -962,6 +962,7 @@ public class WinoMailCollection : ObservableRecipient, IRecipient<SelectedItemsC
         }
         finally
         {
+            Messenger.Unregister<SelectedItemsChangedMessage>(this);
             Messenger.Register<SelectedItemsChangedMessage>(this);
             Messenger.Send(new SelectedItemsChangedMessage());
 

Wino.Services/MailService.cs

@@ -936,12 +936,43 @@ public class MailService : BaseDatabaseService, IMailService
             }
 
             // Manage "ThreadId-ConversationId"
+            // CRITICAL: In-Reply-To and References headers are essential for threading
+            // They must reference the original message's Message-ID from the MIME headers
             if (!string.IsNullOrEmpty(referenceMessage.MessageId))
             {
                 message.InReplyTo = referenceMessage.MessageId;
+                
+                // Add all previous References first
+                if (referenceMessage.References != null && referenceMessage.References.Count > 0)
+                {
                     message.References.AddRange(referenceMessage.References);
+                }
+                
+                // Then add the message we're replying to
                 message.References.Add(referenceMessage.MessageId);
             }
+            else
+            {
+                // WARNING: Reference message has no Message-ID!
+                // This will break threading. Try to use the MessageId from MailCopy if available.
+                var referenceMailCopy = draftCreationOptions.ReferencedMessage.MailCopy;
+                if (referenceMailCopy != null && !string.IsNullOrEmpty(referenceMailCopy.MessageId))
+                {
+                    message.InReplyTo = referenceMailCopy.MessageId;
+                    
+                    if (!string.IsNullOrEmpty(referenceMailCopy.References))
+                    {
+                        // Parse the References string and add them
+                        var references = referenceMailCopy.References.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
+                        foreach (var reference in references)
+                        {
+                            message.References.Add(reference.Trim());
+                        }
+                    }
+                    
+                    message.References.Add(referenceMailCopy.MessageId);
+                }
+            }
 
             message.Headers.Add("Thread-Topic", referenceMessage.Subject);
         }