A message management service that acts as intermediary between a messaging service and a client device can generate a synchronization data bundle for a message that includes an external message identifier usable to retrieve the message from the messaging service. The message management service can send the synchronization data bundle to the client along with the message, and the client can store the synchronization data bundle for each message in its local data store. The client can later return the synchronization data bundle to the message management service, which can use information contained therein to facilitate synchronization and related operations.