After migrating a user from Exchange 2007 to 2013 one of the public folder email addresses she send as says it is no longer valid.
If I log in as a Exchange 2007 user I can send the message and it is received.
If I send the message from an outside address it errors too.
The email address you entered couldn't be found, this
Remote Server returned '550 5.1.1 RESOLVER.ADR.RecipNotFound; not found'
Original message headers:
Received: from emailserver2013.forsythpl.org (this is our 2013 Exchange server) our legacy serer is still online I am about 30% though my migration process.