HelloWe are using Exchange 2000 and also Exchange 2007 in the same AD.We are planning to move the some mailboxes from Exchange 2000 to third party Mail server and also others move to Exchange 2007We move some mailbox to third part Mail server already, but there is some problem appearLet me provide more information on our problemUser A with mail address A@myCompany.com is moved to third part Mail server, user B with mail address B@myCompany.com is a located on Exchange 2007User A can send mail to user B and user B can send mail to User A without any problem.But when user B (EX07 user) reply the old mail (this mail is send from A when A is still on Exchange 2000) from user A, error appear,-----------------------------------------------------------------------------------Delivery has failed to these recipients or distribution list. The recipients email address was not found in the recipient email system IMCEAEX-_o=First+20ORGANIZATION_OU=Exchange......-----------------------------------------------------------------------------------I think when user B reply the mail, it reply to an address which is an object store in AD. but after migration we remove the mailbox of user A, so that the object also removed, is there any method to solve this problem? Can we change the address of the sender to an internet format (i.e. Modify the sender address with SMTP address A@myCompany.com in the mail) before migration? thx

Those replies are cached LegacyExchangeDN values in the x500 format and that is what Outlook is referencing.You have a couple of options:1. Add those old LegacyExchangeDN values to the objects in AD as x500 addresses so they can be found during directory lookups.2. When replying have the users clear the TO: and explicity choose the address they want to reply to from the GAL. You can use something like admodify to do that in bulk:http://support.microsoft.com/kb/909271How to use the ADModify.NET tool to add an X.500 proxy address to a user accountAdmodify is available from:http://www.codeplex.com/admodifyMore info:http://blogs.technet.com/mbaher/archive/2008/02/17/auto-complete-reply-ability-i-need-my-x500.aspxhttp://www.simple-talk.com/sysadmin/exchange/exchange-e-mail-addresses-and-the-outlook-address-cache/http://blog.scottlowe.org/2007/02/15/preserving-nickname-cache-in-exchange-migrations/http://support.microsoft.com/kb/287623How to reset the nickname and the automatic completion caches in Outlook ( You may want to do this as well)

ThanksI will try and update you later. thx

HelloI just modify the setting and test. it is working. thanks