Boy I whish we could email back to the forum! instead of having to come back here to reply....
I use register.com to manage my domain dns, I only had to register mydomain.com and create an MX account for mail.mydomain.com and also redirected the mail.mydomain.com and mail entries on the hosts section of the e-smith manager to point to the external IP of my server... I'm not an experto on this, but this is how I got it to work...
Hope that helps!