SMTP Server - Certain Internet address not going out.

[horna]

One of my user's is trying to send an e-mail out, but it is getting stuck in our Notes SMTP server (7.0.2-FP1). If I transfer the e-mail to another Notes SMTP server, located at a different site, then the e-mail leaves the Notes SMTP server, and gets delivered.
I have also sent a test e-mail from my Notes account out to, two of my personal outside e-mail accounts, and it was delivered to both mail inboxes with no problem.
I have even changed the DNS servers, located in the notes.ini file, but that does not make a difference either.
Is there something in the Notes SMTP server that is holding, or blocking this particular address?
Thank you for your assitance.

 

[horna]

Ignore the second paragraph.....What I meant to say, was that I took the address in question, and sent an e-mail out from my two outside accounts. This e-mail arrived at the recipient's inbox, so I know the address is OK.

 

[horna]

Latest Update - One opinion is that something in our DSN server is not correct. The other opinion is that the recipient's mail server is doing a "Reverse Lookup", and is not validating our Notes SMTP Server's IP address.