Great tutorial. I had relaying problems One was the smtp users was not authorized to send mail relay The /etc/pam.d/smtp was missing copying the /etc/pam.d/pop3 and renaming it to smtp worked with the cp ./pop3 ./smtp command worked. The other problem was that user outside of local network could not send mail. The mail server is behind a CISCO PIX 515 firewall. Cisco by default, in its configuration, it has a fixup for the SMTP protocol on port 25. Disabling fixup on port 25 solved the problem.