Migrate to Exchange 2016 - Coexist EV 10 - CAS redirect

Hi all,

As part of a supplier switch (outsourcing)...

I have a situation in which we will migrate from Ex2010 to Ex2016. Parallel to this we will move from one EV 10 environment to a new EV 11 platform (separate EV directory). Exchange 2016 will be placed "within" the existing Exchange 2010 organization (same forest).

I know we cannot connect EV 10 to Exchange 2016. 

I have a question about the following. Once we add Exchange 2016 servers, the clients will start connecting to Exchange 2016 to be redirected to Exchange 2010 CAS when the mailbox is still on Exchange 2010.

I can't visualize how this will work for EV.

I have Exchange 2010 targets in EV 10. Will the tasks on EV 10 still connect to the Exchange 2010 servers, through the 2010 CAS role?

Or will they try to connect to Exchange 2016 and then fail before they get redirected.

I know this is a bit of a complex scenario, but this is unfortunately in the situation we're in.

we don't have any Exchange 2016 servers installed yet.

We need the archive servers to continue to archive on EV 10 during the migration because it will take time to migrate them to the new environment. Once migrated, we use migration tooling to move the archive to the new platform as well.

Any experience / help / tips is really appreciated!