I am just finishing up a migration to a new Exchange 2010 server, from an old 2003 system. It wasn't a "normal" migration, actually -- I created a separate new forest and totally new mailboxes and then manually exported/imported PST files into each mailbox on the new Exchange 2010 server...
More important details:
The old 2003 server was an GC + Exchange 2003, for 'olddomain.com' and also hosted email for a second "newdomain.com"... which was to become our NEW name/company re-brand... but we didn't have new servers yet, so we just hosted newdomain.com on the Exchange 2003 box in the mean time...
So we get new servers going finally, and set them up for the new forest as 'office.newdomain.com' -- 2 servers: exchange.office.newdomain.com and newserver.office.newdomain.com as the GC.
We still want to get emails for olddomain.com (for legacy purposes) so I add that as a second accepted domain into Exchange 2010 and all seemed to be working...
Until someone "replies" to an old INTERNAL email (any internal email that was imported from the 2003 server), it somehow corrupts the outlook NK2 file and from that point forward, ALL INTERNAL emails bounce! External SMTP still works, but ALL internal bounces... if I delete the Outlook NK2 file, it fixes the problem and users can send internal emails once again!
It seems like it's reading some sort of Active Directory attributes from the old emails.. or something.. I don't know enough at this point to further track down the problem and was hoping for some advice!.. here is the bounce error:
Delivery has failed to these recipients or groups:
The e-mail address you entered couldn't be found. Please check the recipient's e-mail address and try to resend the message. If the problem continues, please contact your helpdesk.
Diagnostic information for administrators:
Generating server: EXCHANGE.office.newdomain.com
#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##
(^^^^^^^^^ it references the old domain here at the beginning of this line, then the new domain at the end???)
Original message headers:
Received: from EXCHANGE.office.newdomain.com
([fe80::900a:2390:8831:dbaa]) by exchange.office.newdomain.com
([fe80::900a:2390:8831:dbaa%10]) with mapi id 14.01.0270.001; Mon, 2 May 2011
Content-Type: application/ms-tnef; name="winmail.dat"
From: UserExample2 <email@example.com>
To: 'UserExample1' <firstname.lastname@example.org>
Date: Mon, 2 May 2011 09:07:10 -0700
More potentially important info: I have a 2 way trust between the 2 forests, and I have DHCP set to assign Primary DNS as the newdomain DNS IP, and the Secondary DNS as the olddomain.com DNS IP. The new servers are also configured with their secondary DNS set as the olddomain DNS server. I wasn't planning on totally retiring the olddomain server for another couple weeks and wanted it online at the same time as the new system and have them talking to each other... but I am not sure if this is contributing to the problem or if it's just some weird active directory thing?