Dear Lazyweb, dear Santa Claus,
A patch solving this would add an option to an SMTP transport which allows the transport to set the authentication credentials instead of the authenticator. The transport still knows the host name given to it and can look up the right authentication credentials, while the authenticator only knows the IP address that we are connected to and thus needs to rely on reverse DNS information to look up the credentials. Which leads to numerous kinds of confusion regarding CNAMEs and broken reverse DNS on the ISP side.
So, please dear Santa, give me a patch for that. It shouldn't be too hard to do.