Ok, so I've got a box named websrv1.mydomain.com. It's a web server running ubuntu, apache2, sendmail, etc.

My email is outsourced to a third party. So in my DNS I've got MX set to mx.thirdparty.net. I've no reason to accept incoming mail on my web server, every email should be sent to the third party. This works correctly accept with sending mail from the webserver (aka via cron or console).

So from my web server, if I send an email to [email protected], it just disappears. No errors, nothing in dead.letter, nothing. I can send to any other address with no issues. If I send to [email protected] it's delivered locally which is fine.

1) Doing an nslookup shows the mx record is correct.
2) Running /mx mydomain.com from sendmail -bt returns the correct result.
3) Running sendmail -bv [email protected] returns:

 sudo sendmail -bv [email protected]
 [email protected]... deliverable: mailer esmtp, host mydomain.com., user [email protected]

4) Running 3,0 [email protected], returns:

    3,0 [email protected]
    canonify           input: me @ mydomain . com
    Canonify2          input: me 
    Canonify2        returns: me 
    canonify         returns: me 
    parse              input: me 
    Parse0             input: me 
    Parse0           returns: me 
    Parse1             input: me 
    MailerToTriple     input:  me 
    MailerToTriple   returns: me 
    Parse1           returns: $# esmtp $@ mydomain . com . $: me 
    parse            returns: $# esmtp $@ mydomain . com . $: me 

So I'm at a loss. Sendmail seems to see the mx record, but it's not using it.