Activesync - you don't have permission to sync with this server

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?
David BarmanAsked:
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Adam BrownSenior Systems AdminCommented:
Make sure your 2016 server is the one that is Internet-facing. Exchange 2010 can't proxy connections to 2016 based mailboxes, but 2016 can proxy to 2010. During your migration, though, you'll want to have both servers internet-facing, since some external connections get redirected instead of proxied.

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
David BarmanAuthor Commented:
Both internet facing?  So I would need separate external ips and A records for each?
Adam BrownSenior Systems AdminCommented:
Yes. Exchange 2010 would preferably use while 2016 would use your normal A records. If this isn't set up like that, some users won't have access to Exchange through some methods during the migration period, 2016 users if only 2010 is on the Internet, 2010 users if only 2016 is on the Internet.
David BarmanAuthor Commented:
Do you mean activesync or outlook anywhere users or both?
Seth SimmonsSr. Systems AdministratorCommented:
No comment has been added to this question in more than 21 days, so it is now classified as abandoned.

I have recommended this question be closed as follows:

-- Adam Brown (https:#a42078632)
-- Adam Brown (https:#a42078674)

If you feel this question should be closed differently, post an objection and the moderators will review all objections and close it as they feel fit. If no one objects, this question will be closed automatically the way described above.

Experts-Exchange Cleanup Volunteer
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today

From novice to tech pro — start learning today.