Exchange 2010 to 2016 migration - Is it a requirement to enable Outlook Anywhere on Exchange 2010?

If not, what will happen with users that are already migrated to Exchange 2016 but still have access to a shared mailbox on Exchange 2010?

Will their Outlook client (2010 updated with required patches) connect to their primary mailbox over MAPI/HTTP and simultaneously connect to the shared mailbox over MAPI/RPC ?

Thanks for the feedback!
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Jozef WooSystem EngineerAsked:
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Adam BrownSr Solutions ArchitectCommented:
It isn't a requirement to have Outlook Anywhere configured. Outlook clients that connect to Exchange 2016 when their mailbox is on Server 2010 will be redirected to the CAS Array end point (if it's defined) using RPC/MAPI directly first, then switch to RPC over HTTPS if that attempt fails. It is generally much less problematic to have Outlook Anywhere enabled on 2010, though, since external users are unable to connect to Exchange with Outlook if it isn't enabled, and Exchange 2016 only uses RPC over HTTPS or MAPI over HTTPS and will not do direct MAPI calls for connectivity. (See: https://blogs.technet.microsoft.com/exchange/2015/10/26/client-connectivity-in-an-exchange-2016-coexistence-environment-with-exchange-2010/ )
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MAS (MVE)EE Solution Guide - Technical Dept HeadCommented:
Agree with Adam,
Please enable outlookanwhere.
Worth reading this article as most of the admins make this mistake when upgrading Exchange 2007/2010 to Exchange 2013/2016.
https://blogs.technet.microsoft.com/exchange/2013/05/23/ambiguous-urls-and-their-effect-on-exchange-2010-to-exchange-2013-migrations/
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Jozef WooSystem EngineerAuthor Commented:
Hi Adam & MAS, thanks for the valuable comments.

I will not provide external access to Exchange (except for Mobile Iron which will connect directly to the Active Sync virtual directory by using the IP address and not the FQDN).

I am aware of the ambiguous URLs and I will use a different URL for my CAS Array than for the HTTP workloads. Currently, the CAS Array is mail.company.local and I would prefer to use it on Exchange 2016 so I still have to figure out a way to rename the current CAS Array.

In case I don't enable Outlook Anywhere: I know that users with their primary mailbox on 2010 will get the CAS Array connection point through autodiscover (Exchange 2016 will proxy the autodiscover request and 2010 will answer). However, what about users who have their primary mailbox on Exchange 2016 and a shared mailbox on 2010 (or vice versa!)? Will Outlook be able to open one connection with RPC/MAPI and one connection with MAPI/HTTP (for each mailbox a different protocol since they are on different Exchange versions)?

Thanks again.
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Jozef WooSystem EngineerAuthor Commented:
I have done some tests in my lab environment and enabling Outlook Anywhere does not seem to be required. I have configured an Outlook client with a mailbox on Exchange 2016 and a shared mailbox on Exchange 2010 and I have connections over RPC/HTTP for the primary mailbox and RPC/TCP connections for the shared mailbox. That's the prove for me that it is indeed not required and it also doesn't have any advantages as far as I can see (as long as you don't have external users connecting).
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Jozef WooSystem EngineerAuthor Commented:
I have done some tests in my lab environment and enabling Outlook Anywhere does not seem to be required. I have configured an Outlook client with a mailbox on Exchange 2016 and a shared mailbox on Exchange 2010 and I have connections over RPC/HTTP for the primary mailbox and RPC/TCP connections for the shared mailbox. That's the prove for me that it is indeed not required and it also doesn't have any advantages as far as I can see.
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