My Qmail install on Centos5 has CRAM-MD5 installed.
I want to use this to an authenticated SMTP relay.
Where do I specify the username and password details for QMail?
Assuming you have installed the relative qmail-remote-ath patch (you can find it here) you should add in the file /var/qmail/control/smtproutes
where xxx.xxx.xxx.xxx is the IP for your SMTP relay