I am in the process of migrating from exchange 2007 to exchange 2013.
I have created an external and INternal legacy name space . I have configured the 2013 Cas servers with the internal/external URLs : https://webmail.domain.com and the 2007 CAS servers with the internal/external URLs: https:legacy.domain.com
for all virtual directories.
OWA redirect, from 2013 to 2007 works without any issues. Autodiscover works great and autoupdated all outlook profiles with in the domain.
the only issue i am having is with activesync. If i configure a mailbox on the 2013 server with activesync it works no issue. If i try to use active sync with a 2007 mailbox it fails.
the account is created on the iphone and android without issue.
the problem is when you try to sync i get the error message on all 2007 accounts on phones
" can not get mail, rejected by server"