SMTP authentication is a requirement in many virtual hosting environments these days, since most ISPs and other internet access points (hotels, wireless "hot spots", etc.) now block normal SMTP port 25. Further, TLS is highly recommended to prevent authentication data from being sent unencrypted on the Internet.
Setting these up manually can be difficult and prone to error, and they are very specific to the selected mail server (MTA) and operating system, due to different implementations of PAM, SASL libraries, etc. This would be a welcome feature to have automatically configured in Virtualmin Professional.
Here are a few important links for reference:
<UL> <LI><A HRef="http://www.FAQs.org/rfcs/rfc2554.html">RFC 2554 - SMTP Service Extension for Authentication</A></LI> <LI><A HRef="http://www.postfix.org/SASL_README.html">Postfix SASL Howto</A></LI> <LI><A HRef="http://www.postfix.org/TLS_README.html"></A>Postfix TLS Support</LI> <LI><A HRef="http://postfix.state-of-mind.de/patrick.koetter/smtpauth/"></A>Postfix SMTP AUTH (and TLS) HOWTO</LI> <LI><A HRef="http://www.sendmail.org/~ca/email/auth.html">SMTP AUTH in sendmail 8.10-8.13</A> (for future reference, given that postfix is currently the supported MTA)</LI> </UL>