Cross domain conflicts

The WAN I work with will not allow outlook 2000 to access
a user's profile located in another domain, however all
other privledges function (save internet explorer). Also
outlook functions normally when logged in under the
primary domain, this eliminates a permissions error. I
believe the problem is related to either the firewall, or
global security permissions. If anyone has experience
with this kind of thing I would greatly appreciate the
advice.