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.