Mail Authentication

[gebser]

Finally I got emacs' mail working... to a degree.  I can send mail with
it, but only to users on the same machine.  If I try to send outside
(via my ISP), I get nothing.  That is to say, I know that emacs is
connecting to the ISP and handing off the email, but it never gets
delivered.  I suspect that the ISP is simply tossing it out due to lack
of authentication from me.  I found a couple functions alleged to remedy
that:

     ;; Authenticate using this username and password against my server.
     (setq smtpmail-auth-credentials
           '(("hostname" "port" "username" "password")))
     ;; Use STARTTLS without authentication against the server.
     (setq smtpmail-starttls-credentials
           '(("hostname" "port" nil nil)))
     

For "hostname" I don't know whether to fill in my (the local machine's)
hostname (just the hostname or host.domain.com?) or that of my ISP, or
the one in one function and the other in the second function.  

Also, I use a couple different email addresses (usernames and passwords)
on the same ISP-- how would I handle that in (setq
smtpmail-auth-credentials ...)?

Docs, manpages, and the web all give me nothing.  Has anyone set this up
before?  If so, tips and clues much appreciated.


tia,
ken