How to set smtp server on ubuntu ?

I had an intranet server with Ubuntu 14.04 running on postfix

I wish to set up smtp in order to send notification to users when the pad contents had been changed , as below:

[etherpad.local.properties]
smtpServer = aaa.bbb.ccc:25
smtpUser = username
smtpPass = clearpassword

However, it didn't work, no email was sent.
Is the above setting wrong ? or because of the intranet smtp problem ?
Thanks