Hello,
I have a multi domain exchange 2013. One of the domains was migrated to office 365 and mailboxes and domain was removed from the exchange.
The synchronization is filtered down to the OU where the migrated users are. They only have proxy address and mail attribute.
Now users that are still on the on-prem exchange are unable to send mail to the domain that was migrated to Office 365 with the following error:
Remote Server returned '420 4.2.0 Recipient deferred because there is no Mdb'
I tried setting the migrated domain back into the exchange server as an external relay domain but that did not work. The on-prem exchange is still looking for the mailboxes in its DB.
The exchange is not in hybrid mode.
Any ideas on how I can sidestep this?
Thanks in advance,
Haukur