diff --git a/app/src/main/java/eu/faircode/email/Core.java b/app/src/main/java/eu/faircode/email/Core.java
index 985efc0729..9f1f3840aa 100644
--- a/app/src/main/java/eu/faircode/email/Core.java
+++ b/app/src/main/java/eu/faircode/email/Core.java
@@ -575,6 +575,17 @@ class Core {
         return uid;
     }
 
+    private static void noop(IMAPFolder ifolder) throws MessagingException {
+        // https://tools.ietf.org/html/rfc3501#section-6.3.11
+        ifolder.doCommand(new IMAPFolder.ProtocolCommand() {
+            @Override
+            public Object doCommand(IMAPProtocol protocol) throws ProtocolException {
+                protocol.noop();
+                return null;
+            }
+        });
+    }
+
     private static void onSeen(Context context, JSONArray jargs, EntityFolder folder, EntityMessage message, IMAPFolder ifolder) throws MessagingException, JSONException {
         // Mark message (un)seen
         DB db = DB.getInstance(context);
@@ -745,6 +756,9 @@ class Core {
         // Add message
         ifolder.appendMessages(new Message[]{imessage});
 
+        // Send no operation
+        noop(ifolder);
+
         // Delete previous (external) version
         if (message.uid != null) {
             db.message().setMessageUid(message.id, null);
@@ -845,7 +859,11 @@ class Core {
                 icopies.add(icopy);
             }
 
+            // Add message
             itarget.appendMessages(icopies.toArray(new Message[0]));
+
+            // Send no operation
+            noop(itarget);
         } else {
             for (Message imessage : map.keySet()) {
                 Log.i("Move seen=" + seen + " unflag=" + unflag + " flags=" + imessage.getFlags());