Unable to launch Exchange 2016 mailbox from Outlook 2010 and 2016 - Able to open up via OWA

We are migrating from Exchange 2010 to 2016 and are in a state of coexistence. I'm unable to launch any Exchange 2016 mailboxes from Outlook 2010 and 2016. I am able to open up the Exchange 2016 mailbox from Outlook Web Access. When I try to launch the mailbox from Outlook I get the error "Cannot open your default email folders. Microsoft Exchange is not available. Either there are network problems or the Exchange server is down for maintenance". Any suggestions? I have not cut over autodiscover to Exchange 2016 yet. Is there something I need to configure with Outlook Anywhere for Exchange 2016?
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Jose Gabriel Ortega CConnect With a Mentor CEO J0rt3g4 Consulting ServicesCommented:
You'd need to finish the configuration of certificates, and outlook anywhere in Exchange 2016, Since it is introduced in the topology and the coexistence is in place all the connectivity should go (internally and externally) to the new exchange 2016, it will manage the conectivity internally to the 2010 mailboxes thru 2016
MAS (MVE)Connect With a Mentor Technical Department HeadCommented:
Hi BenSihn,
Please add an host entry in your PC  to Exchange 2016 and try.         mail.domain.com

FYI your interface should be Exchange once Exchange2016 is introduced in the topology and once Exchange2010 mailbox connected to Exchange 2010 server it will not use Exchange 2016 for next connectivity from internal network due to protocol difference.

Richard InnesConnect With a Mentor Senior IT ConsultantCommented:
Are you planning on using the same namespace for your Exchange 2016 server client access URLs? On Exchange 2016 you should configure the SCP and client access URLs with the correct settings and assign your certificate. You will have issues with Outlook connectivity until you switch the DNS for the Autodiscover and client access namespaces over to the Exchange 2016 as you can only connect from a newer version to an older version not the other way round.  For testing purposes to see what the Outlook client is doing you can use the Test-Email Auto Configuration option and enter details of a mailbox that is hosted on 2016.
Ajit SinghCommented:
If this is happening for all the users check RPC client access service on Exchange.
Try to ping autodiscover and outlook array url.


Get the complete detailed about Client Connectivity in an Exchange 2016 Coexistence Environment with Exchange 2010:  https://blogs.technet.microsoft.com/exchange/2015/10/26/client-connectivity-in-an-exchange-2016-coexistence-environment-with-exchange-2010/

Here is another informative article for installing Exchange Server 2016 in co-existence with Exchange 2010: https://frenchitguy.com/installing-exchange-server-2016-in-co-existence-with-exchange-2010/
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