For IMAP and POP3 authentication, all you have to do is change the “Format for usernames that include domain” in:
Virtualmin > System Settings > Server Templates > Default Settings > Mail for Domain
to be “[email protected]”.
However, Cyrus SASL, which is what handles the SMTP authentication, requires a special flag on it to handle [email protected] usernames, a -r in the settings. The magical file you need to edit is /etc/sysconfig/saslauthd. At the bottom you will see the following:
Additional flags to pass to saslauthd on the command line.
See saslauthd(8) for the list of accepted flags. FLAGS=-r
Just make your FLAGS= like mine does. This will pass the -r to the sasl authentication daemon, and your [email protected] authentication will work!
Let me know if you have any other questions.
Originally found at : http://blog.molski.nl/2009/10/07/virtualmin-and-userdomain-pop3smtp-login-style/