Added new Exchange 2016 server. Old Exchange 2010 server is the internet facing server. In the process of migrating mailboxes to the new 2016 server. Users that have been migrated now don't receive any updates on mobile/activesync devices. If I attempt new account setup for one of those users we receive "You don't have permission to sync with this server". What do I need to do so all mailboxes (on both the 2010 and the 2016) can use activesync?