...I think...
I have sendmail configured. I use Webmin for admin purposes (less typing for me, which is good as I am the king of typo town).
If I send an email from the command line... 'cat message|mail -s "Mail Message"
email@address.com' then it will not go through. If (in webmin) i send a message and make sure to add the @domainname.com instead of the default @localhost.localdomain, it does go through with no problems.
I have teh following setup in my sendmail config file. This domain does not recieve mail, only sends.
MASQUERADE_DOMAIN(localhost.localdomain)dnl
MASQUERADE_AS(`domainname.com')dnl
Any thoughts?