We had a zimbra server die on us, and restored on to a new one. To let users grab old mail that was missing from the backup, we managed to get the old server up and running (from a USB drive haha!).

Most people are fine, but we've got one that is giving the following error:

External Account Failure
system failure: Folder sync failed, system failure: Synchronization of folder '/New External Account 1/Personal' failed, system failure: UID FETCH failed: com.zimbra.cs.mailclient.CommandFailedException: UID FETCH failed: Error in response, UID FETCH failed: Error in response, Exception in response handler, system failure: subject too long
What is the limit of the subject, how can I tell which message is causing the error, and why is the error happening at all, given the other server is also a Zimbra server?