diff --git a/app/src/main/java/eu/faircode/email/AdapterMessage.java b/app/src/main/java/eu/faircode/email/AdapterMessage.java
index b6ac6e8b17..274a21964b 100644
--- a/app/src/main/java/eu/faircode/email/AdapterMessage.java
+++ b/app/src/main/java/eu/faircode/email/AdapterMessage.java
@@ -298,6 +298,7 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
     private boolean language_detection;
     private List<String> languages;
     private static boolean debug;
+    private int level;
 
     private boolean gotoTop = false;
     private Integer gotoPos = null;
@@ -1399,6 +1400,8 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
                 tvError.setText(text);
                 tvError.setVisibility(View.VISIBLE);
             } else {
+                if (BuildConfig.DEBUG && level <= android.util.Log.INFO)
+                    error = message.thread;
                 tvError.setText(error);
                 tvError.setVisibility(error == null ? View.GONE : View.VISIBLE);
                 ibHelp.setVisibility(error == null ? View.GONE : View.VISIBLE);
@@ -6154,6 +6157,7 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
             languages = null;
 
         debug = prefs.getBoolean("debug", false);
+        level = prefs.getInt("log_level", Log.getDefaultLogLevel());
 
         DiffUtil.ItemCallback<TupleMessageEx> callback = new DiffUtil.ItemCallback<TupleMessageEx>() {
             @Override
diff --git a/app/src/main/java/eu/faircode/email/Core.java b/app/src/main/java/eu/faircode/email/Core.java
index cae4b2da5e..6504f59dc7 100644
--- a/app/src/main/java/eu/faircode/email/Core.java
+++ b/app/src/main/java/eu/faircode/email/Core.java
@@ -2729,7 +2729,7 @@ class Core {
                         message.references = TextUtils.join(" ", helper.getReferences());
                         message.inreplyto = helper.getInReplyTo();
                         message.deliveredto = helper.getDeliveredTo();
-                        message.thread = helper.getThreadId(context, account.id, 0);
+                        message.thread = helper.getThreadId(context, account.id, folder.id, 0);
                         message.priority = helper.getPriority();
                         message.auto_submitted = helper.getAutoSubmitted();
                         message.receipt_request = helper.getReceiptRequested();
@@ -3615,7 +3615,7 @@ class Core {
                     have = true;
 
                 if (dup.folder.equals(folder.id)) {
-                    String thread = helper.getThreadId(context, account.id, uid);
+                    String thread = helper.getThreadId(context, account.id, folder.id, uid);
                     Log.i(folder.name + " found as id=" + dup.id +
                             " uid=" + dup.uid + "/" + uid +
                             " msgid=" + msgid + " thread=" + thread);
@@ -3701,7 +3701,7 @@ class Core {
             message.inreplyto = helper.getInReplyTo();
             // Local address contains control or whitespace in string ``mailing list someone@example.org''
             message.deliveredto = helper.getDeliveredTo();
-            message.thread = helper.getThreadId(context, account.id, uid);
+            message.thread = helper.getThreadId(context, account.id, folder.id, uid);
             message.priority = helper.getPriority();
             message.auto_submitted = helper.getAutoSubmitted();
             message.receipt_request = helper.getReceiptRequested();
diff --git a/app/src/main/java/eu/faircode/email/FragmentOptions.java b/app/src/main/java/eu/faircode/email/FragmentOptions.java
index 5267c225f5..265104c3a1 100644
--- a/app/src/main/java/eu/faircode/email/FragmentOptions.java
+++ b/app/src/main/java/eu/faircode/email/FragmentOptions.java
@@ -144,7 +144,7 @@ public class FragmentOptions extends FragmentBase {
             "swipe_reply",
             "language_detection",
             "quick_filter", "quick_scroll",
-            "experiments", "debug",
+            "experiments", "debug", "log_level",
             "biometrics",
             "default_light"
     };
diff --git a/app/src/main/java/eu/faircode/email/MessageHelper.java b/app/src/main/java/eu/faircode/email/MessageHelper.java
index a8b123b427..253282f2e5 100644
--- a/app/src/main/java/eu/faircode/email/MessageHelper.java
+++ b/app/src/main/java/eu/faircode/email/MessageHelper.java
@@ -1135,7 +1135,7 @@ public class MessageHelper {
         return (header == null ? null : MimeUtility.unfold(header));
     }
 
-    String getThreadId(Context context, long account, long uid) throws MessagingException {
+    String getThreadId(Context context, long account, long folder, long uid) throws MessagingException {
         if (imessage instanceof GmailMessage) {
             // https://developers.google.com/gmail/imap/imap-extensions#access_to_the_gmail_thread_id_x-gm-thrid
             SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
@@ -1173,23 +1173,24 @@ public class MessageHelper {
             }
         }
 
-        if (thread == null && refs.size() > 0)
-            thread = refs.get(0);
-
-        if (thread != null) {
-            List<EntityMessage> after = db.message().getMessagesByInReplyTo(account, msgid);
-            for (EntityMessage message : after)
-                if (!TextUtils.isEmpty(message.thread) && !thread.equals(message.thread)) {
-                    Log.w("Updating after thread from " + message.thread + " to " + thread);
-                    db.message().updateMessageThread(message.account, message.thread, thread);
+        if (thread == null) {
+            List<EntityMessage> similar = db.message().getMessagesByMsgId(account, msgid);
+            for (EntityMessage message : similar)
+                if (!TextUtils.isEmpty(message.thread) && message.folder != folder) {
+                    thread = message.thread;
+                    break;
                 }
         }
 
         if (thread == null)
-            if (TextUtils.isEmpty(msgid))
-                thread = Long.toString(uid);
-            else
-                thread = msgid;
+            thread = (uid == 0 /* POP3 */ ? msgid : account + ":" + folder + ":" + uid);
+
+        List<EntityMessage> after = db.message().getMessagesByInReplyTo(account, msgid);
+        for (EntityMessage message : after)
+            if (!TextUtils.isEmpty(message.thread) && !thread.equals(message.thread)) {
+                Log.w("Updating after thread from " + message.thread + " to " + thread);
+                db.message().updateMessageThread(message.account, message.thread, thread);
+            }
 
         return thread;
     }