Yeah, telnet is like that; so easy to forget you have to provide a port. Been there, done that too often.
z9m9z is only as complex as it needs to be. I run a number of virtual hosts from it. The challenge here is what has been done to the default Centos postfix configuration by ClearOS.
I took a quick look at /etc/postfix/main.cf and saw that I had set the domain to htt-consult.com. That would convince postfix to do a local delivery. So I changed it to home.htt and ran a test with:
sendmail -i email@example.com < xfce.lst
and that was properly relayed through z9m9z. So the problem was mine in ClearOS in improper configuration of the Mail Settings dialog.
One for your tips and tricks for those that use an external (to ClearOS) mail service. The ClearOS mail domain MUST be different from your external mail service domain.
Oh, and if you want help developing a rich featured email service, I am available.