You cannot point EMM to 2 different Exchange servers unless you set up an additional proxy server. Our EMM Proxy server can only sync mail with one CAS server.
Typically there are a couple of ways that you can do this:
1- The easiest way is to point the EMM Proxy server to the 2013 CAS server. This way users that are migrated to 2013 as well as the ones that remain in 2010 can still sync mail. Refer to KB70053 for changing the EMM proxy server to point to a different CAS. For this process to work on the backend you would have to have your 2013 server and a 2010 SP3 only on the mailbox.
2- You can setup a second proxy EMM server pointing to the new 2013 CAS server and configure a separate policy in EMM to direct mail to that new proxy server. You can then create an AD group for the migrated to 2013 and add this group under the Membership tab of the new policy, save it and publish it. As you start adding those users to the AD group they will update the policy on the device to point to the new proxy server.
Hope this helps.
Not to hi-jack a thread, but this is the closest question/answer I've seen to my problem.
Would this work for Exchange 2003 users being migrated to Exchange 2010? Option 1 seems to be the best one for my orginization.
Unfortunately that won't work. This process is only possible if migrating from Exchange 2007>2010 or 2010>2013. Exchnage 2003 did not use the CAS architecture so a 2010 CAS server cannot process activesync traffic for Exchange 2003 users.
in your case I believe option 2 would be the best viable option or depending on how many users you have if you can migrate them all in a short amount of time you can point EMM to your 2010 environment once all users are migrated.
Thanks for the info. It looks like option 2 is how we'll end up doing it as we can't migrate all the users at one time.