We moved mailboxes from one forest to another. Both servers are Exchange 2010.
One mailbox (and ONLY one mailbox) can't receive external mail.
All firewall, SMTP, Public DNS, routing, etc. is working. All other mailboxes are working fine.
I exported the mailbox to a PST, deleted the AD account and Exchange mailbox and then rebuilt them. I then imported the PST. External mail is still not coming to the user.
Mail is not even hitting the mailbox. Checked OWA.
Load up WireShark and sniff port 25 TCP (or whatever port you receive mail on) and examine the TCP session, see if your server is accepting the mail in good health, or rejecting it for some reason (mistyped recipient email address?)