--- a/autoland/autoland/autoland.py
+++ b/autoland/autoland/autoland.py
@@ -264,18 +264,18 @@ def handle_pending_mozreview_updates(dbc
         on (Transplant.id = MozreviewUpdate.transplant_id)
         limit %(limit)s
     """
     cursor.execute(query, {'limit': MOZREVIEW_COMMENT_LIMIT})
 
     mozreview_pingback = mozreview.MozReviewPingback()
     lando_pingback = lando.LandoPingback()
 
-    updated = []
-    all_posted = True
+    completed = []
+    failed = False
     for row in cursor.fetchall():
         update_id, transplant_id, request, data = row
 
         # Validate the pingback hostname is still present in config.json.
         pingback_url = request.get('pingback_url')
         hostname = urlparse.urlparse(pingback_url).hostname
 
         if hostname == 'localhost':
@@ -305,35 +305,45 @@ def handle_pending_mozreview_updates(dbc
                 pingback_url = None
 
         # Update the requester if required.
         if pingback_url:
             logger.info('trying to post %s update to: %s for request: %s' %
                         (pingback.name, pingback_url, transplant_id))
 
             status_code, text = pingback.update(pingback_url, data)
+
             if status_code == 200:
-                updated.append([update_id])
+                # Success.
+                completed.append([update_id])
+
+            elif status_code == 404:
+                # Submitting system "forgot" about this request; delete it
+                # so we can continuing processing pending updates.
+                logger.info('failed: %s - %s' % (status_code, text))
+                completed.append([update_id])
+
             else:
+                # Treat anything else as a transient failure.
                 logger.info('failed: %s - %s' % (status_code, text))
-                all_posted = False
+                failed = True
                 break
 
         else:
-            updated.append([update_id])
+            completed.append([update_id])
 
-    if updated:
+    if completed:
         query = """
             delete from MozreviewUpdate
             where id=%s
         """
-        cursor.executemany(query, updated)
+        cursor.executemany(query, completed)
         dbconn.commit()
 
-    return all_posted
+    return not failed
 
 
 def get_dbconn(dsn):
     dbconn = None
     while not dbconn:
         try:
             dbconn = psycopg2.connect(dsn)
         except psycopg2.OperationalError: