The Mail Target Agent (MTA) log contains errors like:
4/24/2007 5:31:10 PM CMessage::CopyFromPST Warning -2147219456 Unknown Error. - SYNC_E_OBJECT_DELETED (Microsoft Exchange Server Information Store) File: 'aeMAPIMessage.cpp' Line: '315' (Subject: '1358CC5AC4E5DB4393AC126A59CFC19800000542AE1B', SourceKey: '1358CC5AC4E5DB4393AC126A59CFC19800000542AE1B')
This error occurs when a user (or some process such as a third-party archiving tool) has deleted messages from the target mailbox. This results in tombstones of these message source keys remaining in the target Exchange organization, preventing new messages being created with the same source keys.
1. Delete the target mailbox, purge it from Exchange (for Exchange 2007 refer to https://support.quest.com/kb/44408)
2. Update an attribute on the source mailbox, such as add to the Description field.
3. Wait for the DSA to pick up the change & re-mailbox-enable the target object.
4. Run full resynchronization of the affected mailbox to resynchronize all the mailbox content.