One Mailbox Can't Receive External Email

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.

Thoughts?
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Paul WagnerFriend To Robots and RocksAsked:
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Jermaine BhoorasinghJr. Operations EngineerCommented:
Are you able to get to that mailbox internally
Are you using any Spam filtering?
Do you have any transport rules in place?
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FocISCommented:
Have a look at the transport logs in Exchange Tools - it must be logging something.

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?)
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Paul WagnerFriend To Robots and RocksAuthor Commented:
@Jermaine
Are you using any Spam filtering?

You were on the right track with that. It turns out that the spam filter was screening via LDAP. Since it didn't see the user on the old server (where mail was coming in), it was rejecting the mail. So now I know that when I migrate a user to the new server, I have to create a mail contact on the old one so the spam filter sees it is a valid email address.
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