[Solved] Autodiscover in Hybrid O365 - Exchange 2010

Hello :)

I have a Hybrid Office365/Exchange 2010 configuration. If I create a new mailbox on Exchange 2010 (onpremises) my autodiscover works fine inside my organization. If I configure this onpremises account on my Android phone its works fine (changing mail server from outlook.office365.com to mail.mydomain.com)

BUT....:

Outside my organization when I configure my Outlook 2016 (VLSC version, not Click to run version) and put my email and credentials a Office365 window pop-ups and my credentials are not accepted.

o365_ger.jpg
My question: all new onpremises created mailbox (exchange 2010) need to sync to Office365 cloud too (even without license)??
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adrecalAsked:
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MichelangeloConsultantCommented:
It depends on your setup.

Relevant point is: as long as you have mailboxes on prem you should have your autodiscover point vs on prem Exchange, see here: https://blogs.technet.microsoft.com/rmilne/2016/07/14/office-365-exchange-hybrid-deployments-busting-the-autodiscover-myth/ )

Understanding autodiscover (useful read)
https://www.experts-exchange.com/articles/17339/Understanding-and-Setting-Up-AutoDiscover-for-Exchange-2010-2013.html

Check your setup here
https://testconnectivity.microsoft.com

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timgreen7077Exchange EngineerCommented:
where does the user mailbox reside? is the mailbox on-prem or o365?
adrecalAuthor Commented:
Michelangelo, you did the trick!!
Do you think I had followed this documentation of the DNS and had not noticed the observation about the hybrid environment?

To simplify:
Hybrid Office365/Exchange (2010, 2013, 2016...) NOT change your external DNS CNAME to autodiscover.outlook.com until you have all your mailbox on cloud.
Resolution: Revert back my external DNS (Linux Bind, blahrg) autodiscover CNAME to:

autodiscover TTL 3600 CNAME mail.mydomain.com (where mail.mydomain.com is my external url point to OWA)

Thanks guys, thank you Michelangelo. :-)
adrecalAuthor Commented:
Resolution: Revert back my external DNS (Linux Bind, blahrg) autodiscover CNAME to:

before:
autodiscover TTL 3600 CNAME autodiscover.outlook.com.

after:
autodiscover TTL 3600 CNAME mail.mydomain.com. (where mail.mydomain.com is my external url point to OWA. Look at final point ".")
MichelangeloConsultantCommented:
Glad to have helped!
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