I have been trying for the last week in half to set up post fix as a null/relay only. If I use port 25 I get the following:
Jun 7 10:26:02 pswofford postfix/error[2373]: C1B5EEA0476: to=<patswofford@yahoo.com>, relay=none, delay=337693, delays=337663/30/0/0.07, dsn=4.4.1, status=deferred...