Our client has email addresses under two domains, both managed through the same Exchange instance. I set up server side sync and tested the mailboxes. It worked for all users with a primary email address on one of the domains and failed for all of them on the second. All of the alerts created just say that, "An unexpected error occurred while sending the email message 'Test Message' through the mailbox ..."
None of the Common and recommended resolutions on the Troubleshooting and monitoring server-side synchronization page on TechNet (https://technet.microsoft.com/en-us/library/dn850386.aspx) address how to get more information for this sort of problem (or at least I'm missing it if it does).
Does anyone else have any ideas?