Can someone explain me in simple words the importance of creating legacy.domain.com for the old 2007 server ?
While I can understand why it's required for internal DNS, I don't understand the external one...
After redirecting the mail traffic to a new server on my firewall, while still having mailboxes on 2007, I thought it will work like this:
Client connects to mail.domain.com (new 2013 server) -> 2013 is looking for legacy.domain.com 2007 internally and gets the data from there.
Why do I need external legacy dns entry, especially that it will point at exactly the same IP ?