Sendmail authenticated relay
 

I am administering a e-mail server running RHEL 5 with sendmail 8.13 and using dovecot imap most of the users are going to need to be able to send mail from their laptops and i have no idea what network they will be utilizing. How can I implement a secure form of authentication that will allow my users to receive and only relay with authentication? I have already tried using certificates but then my users cant recieve mail because senders cant authenticate.

You need to allow all mail destined for domains you host to be accepeted no matter where they are connecting from. For your users to relay mail from anywhere you need to setup smtp authentication. These links should help

http://www.joreybump.com/code/howto/smtpauth.html
http://www.sendmail.org/~ca/email/auth.html

Will I also need a RELAY line in my access file for this to work?