Exchange 2016 Outlook Anywhere Will Not Connect To Exchange 2010 Server

Upgrading from Exchange 2010 to Exchange 2016. Everything is connected and communicating. However, whenever we point the external interface to the Exchange 2016 server, Outlook anywhere for any mailbox on the 2010 server fails to connect. OWA and Activesync works just fine. Internal connectivity is fine. Just Outlook Anywhere. I have gone through the co-exist configuration, setting Outlook Anywhere to an external, which is my external DNS to our NAT firewall (the only thing I change is the NAT pointer). I have configured Outlook Anywhere on the 2016 server to use NTLM. I have configured IIS on the 2010 server to use both basic and NTLM. Any advise on configuration would be appreciated.
Donald StewartManager of ITAsked:
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Ibrahim BennaTechnology LeadCommented:
Have you removed the external URL from the 2010 server? If the 2010 CAS server has an external URL configured, it will try to redirect clients to that URL and potentially will fail.

What result do you get when you test it using the remote connectivity analyzer?

BTW what version of Outlook at you using?
Are you able to create a new profile for a user with mailbox on 2010 externally?
Donald StewartManager of ITAuthor Commented:
Ibrahim, thanks for the response.

Interesting response. I'll give it a try tomorrow. Interesting, a lot of the procedures say to set the external URL.

I'm using Outlook 2010, 2012, and 365 (local install). I ran the analyzer and it finds the autodiscover, but fails to obtain mailbox configuration. I have tried repairing accounts, and creating new ones. Same issue. I notice that, if I connect to Exchange configured to the 2010 server, then change the NAT to the 2016, it will continue to remain connected until I close Outlook and open it again. As soon as autodiscover kicks in, it breaks.
Ibrahim BennaTechnology LeadCommented:
One more thing - have you changed autodiscover externally to point to Exchange 2016? You need to make sure that all your external client connectivity is going through 2016 as it is able to perform a proxy to 2010.

I believe I also may have misspoken - the external URLs need to be null for all virtual directories (OWA, ActiveSync and such) but it needs to remain for Outlook Anywhere. Check the authentication method for Outlook AnyWhere ( Can you also post the results from the connectivity test site (hide your domain name if necessary)?

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Peter HutchisonSenior Network Systems SpecialistCommented:
Outlook Anywhere for Outlook 2016 now uses MAPI over HTTP rather than RPC over HTTP. Also, the settings for Outlook Anywhere have been removed in the Account Settings in Outlook 2016. So to get it to work with Exchange 2010 requires some changes in the registry on client for

Donald StewartManager of ITAuthor Commented:
Peter: I'm aware of the change in Exchange 2016 as far as communication. The clients with Outlook 2016 have been working fine (and still do) With the Exchange 2010 server. The issue is between Exchange 2016 and Exchange 2010. Thanks

Ibrahim: I used the link you provided and verified the settings in the article. They all appear to be the same as I had, but I went ahead and reran the shell commands and reprogrammed it. When configured to talk to the Exchange 2016 server, clients don't have any issues with OWA and Active Sync, just Outlook Anywhere. I can see on the client Outlook Connection Status trying to connect, but drops, like it is a permission issue. I has one or two connections, but fails to get the third or fourth. Looks like it can not get the proxy. I'm going to reconfigure to use Exchange 2016 again this morning, and I'll get you a screen shot of the Test E-mail AutoConfiguration. The link,, you provided doesn't work anymore. The only thing I notice is Outlook Anywhere in 2016 uses NTLM, while Outlook Anywhere in 2010 uses Basic. The both use both for IIS (which should be the inter Exchange communication). The two servers are talking because I can see email in the transfer queues. Thanks
Vidit BhardwajAdminCommented:
If you are using outlook anywhere and if the mailbox is on 2010, when performing autodiscover it will reach to your 2016, 2016 will be able to give outlook anywhere hostname to the client, hence make sure you set external hostname on OA in 2010 exchange
Donald StewartManager of ITAuthor Commented:
Thanks for all the help. I did review the article Ibrahim pointed out and ran all the shell commands again. This time it appeared to work. However,, over the weekend, I did discover that some (not all) of the external OA clients would connect but not able to send. Running the Test Auto Configuration in Outlook repairs Outlook and it now works. Until the next reboot, then you have to run the Test Auto Configuration again and all is well. Not sure about this. Monday, I'll work with the user and reinstall the account and see if it fixes permanently. This one is weird.
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