I run Postfix on Debian Testing and I originally set outgoing mail in my mailer (Balsa) to be SMTP localhost:25.
I have the choice of sending external mail either through my ISP's mail server or my web site hoster's mail server.
In my Postfix main.cf I had relayhost = (one of two mail servers)
Before I changed ISPs recently I used to send my external mail through my ISP (unauthenticated) but then I changed to my web site hoster's mail server and mail was going out through them (also unauthenticated).
When I changed ISPs recently I found that I could no longer send through my web site hoster's mail server and they say that's because it requires authentication. I don't know why it should have worked with my old ISP and the people who host my web site haven't offered any explanation.
So I'm trying, and failing dismally, to use SASL for SMTP authentication.
I followed these instructions http://linuxgazette.net/142/pfeiffer.html
However if I now try sending mail with SASL set up authentication fails on whichever external mail server I use but I don't know why or how to find out why it's failing.
Can anyone help with this?