Single Recipient Not Receiving External Mail - Exchange Server 2003

Have Server running Windows Server Std 2003
Server is also Domain Controller (Has AD installed on it)
Server has Exchange 2003 installed and running
Working correctly

Have a single user that cannot receive external email
Same user can receive internal email no problem
Same user can send email out

When you send a message you get recipient not found, but she is there and so is her mailbox, as listed in AD and in Exchange System Manager>Admin Groups>First Admin Group>Servers>Servername>First Storage Group>Mailbox Store>Mailboxes>Her Mailbox

There are over 100 users on this system, all others working correctly.
Mailbox appears to be good
User account appears to be good (User logs in and works all day successfully, just no incoming email from outside)

Any ideas what the issue is and/or where to look?
Troubleshooting steps?
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double check user's mailbox setup to make sure both external and internal SMTP domains are ....

Check the mail flow, check user rules if any.
Same email l address used internally and externally sent?

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tech911Author Commented:
Yep -

SMTP Internal setup - works
SMTP External setup - no good
No mailflow rules, if there were, they would impact other users
Internal and External addresses are different, one using the local domain name (internal) and one using an external domain name (external)
Check what happens to an email from an external source addressed to this individual.  look at the smtp logs.
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Have you tried deleting the user and recreating their account?  You'll need to archive the users mail history to a PST file first in order to preserve their mail.
I am puzzled why a delete is seemingly a suggestion at all, possibly this was done previously and the mailbox for the old user (Sid) exists on the exchange side, but can not deliver because of the Sid mismatch.
tech911Author Commented:
That was actually where I was heading, that something is corrupted and it is just not recognizing the user at all.

Seems to be the consensus... Any other ideas are welcome.
Was anything done prior to this issue arising to the user's mailbox/ad account?
What does the SMTP log have on the incoming side? Double check the user's mailbox email setting.
Since it is only affecting this users the issue is possibly with a user based filtering rule.
Do you have a single SMTP setting within each user or there are one internal domain and one external domain?
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