Platform is Windows 2008 R2, Exchange 2010 SP3
Started when we lost a drive in our RAID array. Replaced drive and 10 hours later it was rebuilt.
Do to problems with the Exchange DB, I created a new DB and moved all mailboxes. It appears right now we have this problem with two users. Doesn't matter whether it's internal or external email. Both users can send emails
Have followed other solutions i.e., clearing auto-complete and creating an X500 address. (Seems this has been the fix for many who have dealt with this problem).
Deleted one of the users, then created user and mailbox, still the same problem.