If you’ve been here since before we moved to the new Exchange server last summer, consider recreating any distribution lists you’re using. There have been several instances of bounce-back emails when using a distribution list (or contact group in MS parlance). When you do, it’s better to pull the names for the list from the “Address Book” (global address list; current data on everyone) rather than your “Outlook Contacts” which may have stale data. Let me know if you have any questions.
Thanks,
Stephen