A good article to start with is Exchange 2013 interoperability with legacy Exchange Versions by Michael Van Horenbeeck. A single Exchange 2007 server and a single Exchange 2013 server. So I usually setup some dummy URLs on the 2013 side and test all the connections (OWA, EAS, OA).This article points out when Exchange 2013 will proxy connections to 2007 vs. Both servers are installed in the same Active Directory Site. This way I know all proxying and redirecting is working prior to making any user impacting changes.Introducing Exchange 2013 into an Exchange 2007 environment can be a challenging task.One of the most overlooked, and least documented topics I see is the proper configuration of URLs for Proxy and Redirection. I wouldn’t worry about that little guy.” Yes, I personally like to test everything prior to making any change to the existing 2007 environment.This guide is targeted towards end-users and administrators of Small and Medium Business organizations (SMB).Note: As all the methods discussed are fully supported by Microsoft, they can also be applied to larger corporate environments but for such installations it is best to follow the Preferred Architecture guidelines from the Exchange Team and use a dedicated Autodiscover subdomain with its name on the SSL certificate instead of a redirect.
All discussed solutions are fully supported configurations by Microsoft and do not require any changes to Exchange or the need for a new SSL Certificate.I’m putting in Exchange 2016 onto a new server running Server 2012.Post install the NEW server will hold client access, and mailbox roles.The first step in the migration process is to update these values so that all users connect to OWA, EAS, and OA via Exchange 2013. OWA – (Redirect) Should be pretty straight forward.Again, I won’t go into the details of why, but essentially Exchange 2013 can proxy and redirect back to 2007, but 2007 cannot proxy forward to Exchange 2013. When a user whose mailbox still resides on 2007, accesses OWA via the 2013 CAS, they will be redirected back to 2007 via external URL value: https://legacy.domain.com/owa Active Sync – (Proxy) I prefer to force Active Sync to proxy from 2013 to 2007 as some Active Sync devices don’t handle the redirect correctly.