Question : 5.7.1 Recipient address rejected Access denied, after user name change due to marriage

Performed a rename of a user account in AD (Windows 2003 domain) and GAL is updated & mail flow appear to work internally.  However, when sending to the users NEW address using an ouside email account, I receive an NDR with the followinig "5.7.1 Recipient address rejected Access denied'.  The message appears to be getting rejected at the site where our MX record is hosted.  Here is the 'final recipient', detail within the header:
................................
Final-Recipient: RFC822; main.com>
Action: failed
Status: 5.2.0
Remote-MTA: dns; mail0.ourdomain.com (insert IP address of MX record host here)
Diagnostic-Code: smtp; 554 5.7.1 main.com>: Recipient address rejected: Access denied
.............................................

What could be causing this NDR exclusively from outside addresses?  Thanks for your insight!

Answer : 5.7.1 Recipient address rejected Access denied, after user name change due to marriage

Are you using a third-party spam filter prior to mail reaching your server?  Some of these require that the user be "registered" on them or it will not forward email.  In this case, your user would have a new ID.