We currently have a stand alone install of Exchange 2003 on Server 2003 fully updated in all respects. I have installed Exchange 2007 on Server 2008 fully updated in all respects. I am clearly missing something that I hope is easy. After the install I migrated one mailbox (my own) over to Exchange 2007 and everything worked fine. I sent an e-mail to my co-worker internally and sent an e-mail to my hotmail account and then back into my exchange mailbox and everything was good to go. I left for the night and the next morning I see all e-mail are somehow stuck in the queue. The error was "A local loop was detected" Basically nothing has worked right from the that point on. I finally deleted all send and receive connectors and my Exchange 2003 is now fully functional. What send and receive connectors do I need to configure exactly in order for both these systems to be functional long enough for me to migrate all users to 2007. Also how exactly does the e-mail get sent out during this "coexistence" does all e-mail get sent out my 2003 Exchange?