This is what pop up if no authentication:
------------------------------------------------------------
Sending failed:
Message sending failed since the following recipients were rejected by the server:
jaffaizal@gmail.com (The server responded: "<jaffaizal@gmail.com>: Recipient address rejected: Relay access denied")
The message will stay in the 'outbox' folder until you either fix the problem (e.g. a broken address) or remove the message from the 'outbox' folder.
The following transport protocol was used:
PLANIMA
------------------------------------------------------------
There is a lot in /etc/postfix/main.cf (which part do you want to know?)
JafFaizal