I've run across a reproducible problem while using Microsoft's IIS
6.0 SMTP server.  If I try to send email to a domain whose 'MX'
record points to an 'A' record in another domain, it ignores the MX
records and sends to the 'A' record of the domain (not the A record

In exchange 2003 our organization set up an external smtp relay in the SMTP
protocol of the server complete with ip and login.
In exchange 2007 the protocol access is removed. However there is a SMTP
connector section in hub transport. We configured the use of an external SMTP