We send [bulk] e-mail on behalf of clients aswell as our usual company e-mail via Exchange 2003.
I have two SMTP connectors, one set to reject all e-mail except from certain e-mail accounts which have client’s e-mail addresses as their primary address. E-mail delivered via this route is sent directly via DNS.
We then have another SMTP connector which by default accepts all e-mail but has a higher cost. This connector delivers e-mail via MessageLabs which in turn adds our company disclaimer on the bottom.
However things weren’t working as expected and only one connector would ever get used. I’ve been pulling my hair out over this one for months and today found this article: http://support.microsoft.com/default.aspx?scid=kb;en-us;Q277872
It seems Exchange doesn’t bother to check the rules! – Worse still it hasn’t since Exchange 2000, lets see if Exchange 2007 is any better.