How to password an SMTP server

[Jon D. Slater]

Hi All,

I'm using my FC4 box as a mail server (and also running Mailman).

It's starting to look like I may need to open up the SMTP server to 
"outside access".

Since I don't want to become a SPAM gateway, I'd like to restrict access 
to just a few people.  But, there's a catch.

Some of my "customers" uses a dial-up connection and aways appears from 
a different IP address every time they connect.  So adding them to the 
allow/deny list could be tricky.

How do I get the SMTP require a password?  And, is that secure enough to 
keep spammer's from using my mail server?

Thanks!

Jon