Relay control in sendmail for roaming users

[Bob Brennan]

I have an FC3 mailserver/webserver machine that I am trying to set up
so that users of various web/mail domains on the machine can send and
receive email through their preferred MUA (Outlook/Evolution/etc). The
machine has the latest Sendmail and Dovecot running, with Squirrelmail
supplying access to email for all domains, sending and receiving
properly because it is on the machine itself.

The problem comes when a remote machine or webmail wants to send to
another remote machine, say me at mydomain.com on a remote Outlook to
me at gmail.com, which is "remote relaying". I would use the
pop-before-smtp option that all MUAs now use for authentication.

http://www.sendmail.org/~ca/email/roaming.html#POPB4SMTP is the best
advice I can turn up so far but it seems to be conflicting opinions
and incomprehensible to anyone but Sendmail gurus.

Since pop-before smtp through Sendmail is very common out there -
there must be someone who knows how to make it work step-by-step, or
an idiot's guide on how to do it. I understand the reasons for distros
to enable Sendmail in a mode that locks out spammers but there must be
a secure _working_ mode as well that even a relative newbie can set up
and still be secure(?)

Any advice / insights appreciated,
bob