Automatic email relay agent?

[Hongwei Li]

Hi,

Is there any program that can function as "automatic email relay" agent? 
Basically, I stop all email relay in my fc3 and fc4 systems and allow only
some ip address range to relay emails.  This way, my users in our subnet and
some users at home (who's ip addresses are known) can use outlook etc. to send
emails.  The problem is that sometimes, some users travel to other cities and
they still want to use outlook to send emails.  Since I don't know thoses ip
addresses, they will get "email relay error".

Is there any program that can temporarily add those ip addresses to the
allowed list for email relay for the users with correct password, but not for
other strangers, for some days, then later remove it?

I remember somebody mentioned such package, but never used it and don't know
if it works under fc3, fc4 with selinux enforced.

I appreciate any help!

Hongwei Li