We are currently doing an Exchange migration from 5.5 to 2003 Exchange Server. Two of the user mailboxes that we have just moved have suddenly have issues replying or forwarding emails with or w/o attachments. They received the following error messages:John xxx on 4/26/2007 4:02 PMThe e-mail system was unable to deliver the message, but did not report a specific reason. Check the address and try again. If it still fails, contact your system administrator.The MTS-ID of the original message is:c=US;a= ;p=xxxx xxxx;l=XXXX-070426200158Z-1638MSEXCH:MSExchangeMTA:XXX:XXXXXThey can send new messages to email addresses that they were replying to. Mostly the recipients are internal users, but there are a few external recipients that having the same issue.Thanks You in Advance!Santiago