Barry Samuels bjsamuels@beenthere-donethat.org.uk wrote: [...]
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?
Not with so little information! Use the options in your main.cf under "DEBUGGING CONTROL" to get postfix to log more detail about why it's failing and then send the list the relevant log messages...
Also, have you checked you can AUTH with those servers manually? The article you're using linked http://qmail.jms1.net/test-auth.shtml which looks a fair enough howto.
Good luck!