we have setup "collabration Suite" in our office which hosts our client's emails

we also have exhcngae server which hosts our emails

Collbration suite is on DMZ port of firewall while exchnage is on LAN side.

Any users from collabration suite can not send email to exchange domain address.

Any ideas please?

Thanks

mx

sounds like a problem with DNS entries to me.  How are they trying to send mail to your exchange folks?  Which server do you actually receieve outside email with? Collaboration? If so sounds like your exchange server doesn't have DNS entries for your collaboration server to find your exchange server with.

if that makes since.. I'm doing this trying to walk out the door to go home.  Let me know and i'll try to follow up.. just add some additional info so I can try to give you some 2 cents.