Last week we performed an inter-forest migration to a new domain but kept the same primary smtp addresses. I created mailboxes on the new Exchange server and exported the old mailboxes as psts and imported them to the corresponding mailboxes on the new server. We can send new emails to each other without issue (baring auto-fill which I have placed a workaround so their history is cleared) but when we reply to messages from before the domain cut-over we receive
IMCEAEX _O=NAME+20OF+20ORGANIZATION_OU=EXCHANGE+20ADMINISTRATIVE+20GROUP+20+28FYDIBOHF23SPDLT+29_CN=RECIPIENTS_CN=FIRSTNAME+20LASTNAMEBCC@email.com
#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##
When looking this error up I get a lot of info about X500 records which didn't exist for many of the users on the old domain. I understand that the error means that it is hitting the server and the server doesn't know where to send the mail but why not? Shouldn't it just be using the smtp address? I should mention that from non-outlook programs it works fine. From phones it works fine, but from OWA or Outlook we just get the bounceback error message.
Best Answer
The behaviour you are seeing is what I would expect.
You have gone cross forest, so everyone has a new mailbox in a new domain. Hitting reply to old emails will give you invalid address. If you hit reply, then delete the recipient from the To line and find them fresh from the GAL, then it will work.
This article from the SBS team explains the problem as well (ignore it is SBS, Exchange is the same underneath). http://blogs.technet.com/sbs/archive/2009/05/21/cannot-reply-to-old-emails-or-modify-old-calendar-items-after-pst-mail-migration.aspx