Using sendmail w/ username & password?

[Michael Richard <richar01_(_at_)_gel_(_dot_)_ulaval_(_dot_)_ca>]

I'd like to use my smtp server from an outside network.  Obviously, I get an
error message saying something like "relaying denied" (I didn't try, but we
all know that it will happen if I do).  As I can connect from many different
addresses, I don't want to allow relaying from a large range of IPs.

The solution that comes in mind is to use username and password to prove to
my server who I am, but I didn't find how to implement this solution (if it's
possible at all).

Suggestions?  Comments?  Please tell!

Michael