Does it look something like the below?
If so thats just postfix/amavis/spamassassin blocking spam.
If not then we would need to see some log files to determine
what the problem is. Ive used this setup on my server and its
Im assuming you have verified all programs are running and
ran netstat -tap to see that they are listening on their respective
ports. (and of course that the ports are open).
mail postfix/smtpd: connect from \ 200-127-43-70.cab.prima.net.ar[126.96.36.199]
mail postfix/smtpd: NOQUEUE: reject: RCPT from \ 200-127-43-70.cab.prima.net.ar[188.8.131.52]: 550 5.1.1 \ <firstname.lastname@example.org>: Recipient address rejected: User unknown in virtual mailbox table; from=<email@example.com> to=<firstname.lastname@example.org> proto=SMTP helo=<svnigeg>
mail postfix/smtpd: lost connection after RCPT from 200-127-43-70.cab.prima.net.ar[184.108.40.206]