I'm currently doing mailbox moves from my 5.5 to 2003 server but occasionally run into a snag. Sometimes the mailbox will move fine, but then if someone sends them internet mail they will receive an NDR. Internal mail works fine. Your message To: Mike Green Sent: Fri, 6 May 2005 13:31:19 -0700 did not reach the following recipient(s): Mike Green on Fri, 6 May 2005 13:31:25 -0700 Unable to deliver the message due to a communications failure The MTS-ID of the original message is: c=us;a= ;p=corporate;l=MAIL010505062031KGZ7HXL4 MSEXCH:MSExchangeMTA:Irvine:MAIL01 It would appear that restarting the MTA on Mail01 (Exchange 5.5 server) will get things going again, but that shouldn't be happening. Thoughts?