i am trying to run an 2000 exchange server i have ports 110, 25, 143, 389 all forwarded to the machine i am able to send emails inside the system, but cannot send emails outside the system emails from outside the system do get received into the server when i do send out an email i get an autoresponse from the exchange server saying that: The following recipient(s) could not be reached: harel_zahavi@xxxxxxxxx on 9/9/2002 1:04 AM There was a SMTP communication problem with the recipient's email server. Please contact your system administrator. <Server1.LVI-Domain #5.5.0 smtp;551 Not a valid mailbox> my question here would have to be since i am using a different email address that is smtp address then the actual domain is that causing the problem? or is it a dns problem since i am able to receive on the smtp address? any ideas anyone? please help would be greatly appreciated