Cannot send to specific external email address, cannot find smtp logs

The server in question is Exchange 2003, in a single server environment.

I have an email address on an external domain I am trying to send to.  When I use outlook/exchange to send the person never receives the mail.  No rejections come back to me.  I can telnet from the exchange server to their mail server...and the message sends fine.  I can also send to other email addresses on the same domain as the one who never receives my email.  

There are no filters in place (I have access to the receiving email account).  
I can successfully send/receive to the external address from other accounts (not on my server).
I can send to the external account from a telnet session on my Exchange server.
I can send to other accounts on the receiving domain without trouble.

The issue is when I try to send to this external account from Exchange (Outlook or OWA).  They just never receive it.

Any suggestions would be appreciated, including how to view the SMTP connection logs (if they exist?).  I would love to see the "helo, rcpt to, data, etc..." that Exchange sends to the receiving server so I can determine what is happening.  As I said...it works fine from a telnet session so I know their server isn't blacklisting us.  Furthermore, the client has no rules on her mailbox preventing email being received from me.

Tips...?