We currently have an Exchange 2003 server running in our Administrative domain. There is an Exchange 5.5 server running in the same site that is on its way out. We have deleted the Internet Mail Connector on the 5.5 box and all mail is being sent to and through the 2k3 server. We also have a Sunbox running sendmail that contains the aliase list for everyone on campus. The Excahnge server is supposed to be sending everything to the sunbox and the sunbox sends everything to the recepient (theoretically). There is an I-Mail server that runs the student mail sitting on an NT 4.0 domain controller in the Academic domain. Both domains are running AD in mixed mode. The problem is that our POP3 users who are on the Exchange server (staff and Faculty) cannot route mail through the exchange server. We have a connector in place that points all mail to the sunbox. POP3 users can send mail to off campus addresses but when they send mail to a student (in theis case akorruthu@xxxxxxxxxxxxxxxxx) we get an NDR stating that "The e-mail account does not exist at the organization this message was sent to. Check the e-mail address, or contact the recipient directly to find out the correct address. <adm03.admin.austincollege.edu #5.1.1 smtp;550 5.1.1 <akorruthu@xxxxxxxxxxxxxxxxx>... User unknown>". adm03 being the name of the Exchange 2003 server. It looks as if adm03 is trying to resolve the address itself instead of routing everything to the SMPT gateway. people using Outlook to access adm03 are not having a problem sending mail to students. Just my POPpers and IMAP4 users which are mostly MACs.