Well, found the answer here.

http://sdb.suselinux.hu/en/sdb/html/rsimai_imap_smtp_auth.html

-----Original Message-----
From: Jim & Toni [mailto:jntdibb@bellatlantic.net]
Sent: Monday, October 13, 2003 2:28 PM
To: 'wlug@wlug.org'
Subject: Authentication on outgoing SMTP, how to set with postfix?

I’ve almost got postfix setup as a mail relay from my local linux box to ‘outgoing.verizon.net’. But, the postfix howto doesn’t specify how to provide login/password authentication for smtp servers that require it. The error was ‘554: Authentication required’

Going to search more, but appreciate any help.

Thanks.