fix: delete superseded draft UID after sending via SMTP

Signed-off-by: Sebastian Krupinski <krupinski01@gmail.com>

lib/Providers/Service.php

@@ -675,10 +675,27 @@ class Service implements ServiceBaseInterface, ServiceMutableInterface, ServiceC
             // ignore — the message was already delivered
         }
 
+        // Best-effort: IMAP has no native "submit existing draft" operation, so the
+        // message above was always sent fresh. If it originated from a synced draft,
+        // remove the now-superseded draft UID. A failure here must not turn a
+        // successful delivery into an error; the draft is simply left for a later
+        // discard or retry.
+        if ($source !== null
+            && $source->provider() === $this->provider()
+            && $source->service() === $this->identifier()) {
+            try {
+                $this->initialize();
+                $this->remoteService->entityDestroy($source->collection(), (int) $source->entity());
+            } catch (\Throwable) {
+                // ignore — the message was already delivered
+            }
+        }
+
         return new EntitySubmitResult(
             disposition: EntitySubmitResult::DISPOSITION_SENT,
             transportId: $queueId !== '' ? $queueId : null,
             sentEntity: $sentEntity,
+            sourceDraft: $source instanceof EntityIdentifier ? $source : null,
         );
     }