Mail from my server sent to earthlink bounce with the message There was a SMTP communication problem with the recipient's email server. Please contact your system administrator. <xchange2.bio.hunter.cuny.edu #5.5.0 smtp;550-EarthLink does not recognize your computer> My guess is this is because earthlink is seeing my server as its domain.local name (xchange2.bio.hunter.cuny.edu ) instead of its external DNS name which would be genectr.hunter.cuny.edu. Is there a way to make sure my server communicates using its external DNS name Lloyd Williams