SMTP authentication

[Matt Simonsen]

Is it possible/adviseable to run a Qmail server to authenticate all relay
SMTP traffic so that we can leave the relay open but not allow spammers
access? I have Qmail running with Courier IMAP server, my problem is that we
have some users with laptops who travel and use different ISPs out of the
office and would not be able to get email through out SMTP server. To ask
them to change settings may be too much. I have thought of setting up 2
Outlook profiles for them with different outgoing mail servers, but I am
hoping there is a way to allow their traffic through via a username and
password combo.

Thanks
Matt