I am currently using hMail with Helm/Windows.

hMail only allows one HELO address. This means that all the domains share the same HELO.
This makes multiple IPs on the server useless for SMTP, since if I use another IP (other
than the one in the HELO) emails from that domain will be rejected by many servers.

Any email servers for windows that allow you to specify HELO per domain?

It does not have to be free (although it would be nice).

Thank you for your suggestions!