Improving thread mapping for all synchronizers.

2026-02-23 01:51:44 +01:00
parent c5a631da6f
commit 79a81710f0
7 changed files with 314 additions and 60 deletions
@@ -114,6 +114,7 @@ public static class MailkitClientExtensions
        var fromAddress = mime != null ? GetActualSenderAddress(mime) : GetEnvelopeSenderAddress(envelope);
        var references = mime?.References?.GetReferences() ?? messageSummary.References?.GetReferences();
        var inReplyTo = mime != null ? mime.GetInReplyTo() : envelope?.InReplyTo ?? string.Empty;
+        var threadId = ResolveThreadId(messageSummary, messageId, references, inReplyTo);
        var hasAttachments = mime != null ? mime.Attachments.Any() : false;
        var itemType = mime != null ? GetMailItemTypeFromMime(mime) : MailItemType.Mail;

@@ -121,7 +122,7 @@ public static class MailkitClientExtensions
        {
            Id = messageUid,
            CreationDate = creationDate,
-            ThreadId = messageSummary.GetThreadId(),
+            ThreadId = threadId,
            MessageId = messageId,
            Subject = subject,
            IsRead = messageSummary.Flags.GetIsRead(),
@@ -141,6 +142,48 @@ public static class MailkitClientExtensions
        return copy;
    }

+    private static string ResolveThreadId(IMessageSummary messageSummary, string messageId, string references, string inReplyTo)
+    {
+        var serverThreadId = messageSummary.GetThreadId();
+        if (!string.IsNullOrEmpty(serverThreadId))
+            return serverThreadId;
+
+        // Fallback threading for IMAP providers that do not expose a native ThreadId:
+        // - Prefer root of References chain
+        // - Then In-Reply-To
+        // - Finally own Message-Id (single-message thread root)
+        var rootReference = references?
+            .Split(new[] { ';', ',', ' ', '\t', '\r', '\n' }, StringSplitOptions.RemoveEmptyEntries)
+            .Select(NormalizeThreadToken)
+            .FirstOrDefault();
+
+        if (!string.IsNullOrEmpty(rootReference))
+            return rootReference;
+
+        var normalizedInReplyTo = NormalizeThreadToken(inReplyTo);
+        if (!string.IsNullOrEmpty(normalizedInReplyTo))
+            return normalizedInReplyTo;
+
+        var normalizedMessageId = NormalizeThreadToken(messageId);
+        if (!string.IsNullOrEmpty(normalizedMessageId))
+            return normalizedMessageId;
+
+        return string.Empty;
+    }
+
+    private static string NormalizeThreadToken(string value)
+    {
+        if (string.IsNullOrWhiteSpace(value))
+            return string.Empty;
+
+        value = value.Trim();
+
+        if (value.StartsWith("<") && value.EndsWith(">") && value.Length > 2)
+            value = value.Substring(1, value.Length - 2);
+
+        return value;
+    }
+
    private static string GetPreviewText(IMessageSummary messageSummary, string subjectFallback)
    {
        if (!string.IsNullOrWhiteSpace(messageSummary.PreviewText))