I recently migrated from Exchange 2010 to 2013; moved all mailboxes, setup certificates and everything is great.
I wanted to remove the old server when I noticed there are 3 mailboxes (fed and 2 system) that I forgot to migrate. I came to do so only to realize that I had already demoted the server (it was AD DC as well) therefore the new server no longer sees the old server and migration of mailboxes fails.
Do I have to move these mailboxes? If I do how would I do that when the new server doesn't see the old one (pinging it by the server name works but pinging by full name doesn't). And if I don't, how would I go about removing the old server? I tried to remove the database but it won't let me due to these mailboxes residing on the old database. I don't want to just shut off the older server since the objects will remain on the 2013 server.