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AtanasM's avatar
AtanasM
Iron Contributor
Apr 21, 2020
Solved

MS Teams with Exchange On-Premises

MS Teams is unable to connect to Exchange calendar on Premises. The calendar icon is unavailable in Teams. The mailbox is in Exchange on prem, there is a Hybrid configuration and Oauth is working. ...
Exchange On-Premises
teams
  • ThomasStensitzki-MVP's avatar
    ThomasStensitzki-MVP
    Apr 22, 2020

    AtanasM How is the on-premises Exchange Server published to the Internet? Is Windows Server 2016+ Application Proxy used, or another reverse proxy component?

    In regard to the Exchange hybrid configuration, is AutoDiscover DNS used or does the Exchange hybrid configuration use a static TargetAutodiscoverEpr?

  • AtanasM's avatar
    AtanasM
    Iron Contributor
    Apr 22, 2020

    Hello oliwer_sundgren 

    I checked many times and Oauth is set up correctly.

    Are you sure, that enabling Group-Writeback can solve the issue?

    Thanks in advance.

    • oliwer_sundgren's avatar
      oliwer_sundgren
      Iron Contributor
      Apr 23, 2020

      HelloAtanasM ! 

       

      If OAuth is set up correctly and your on-prem Exchange server(s) are published correctly towards the internet without special proxies or smarthosts. then Group writeback could be the issue here. It's worth a try 🙂 

       

      I've previously enabled Group-Writeback and got this to work. 
      Since you're in a hybrid, the local Exchange resources usualy needs a reference object in Active directory to route mail and work correctly. 

      Read this Docs article for reference 

      https://docs.microsoft.com/en-us/exchange/hybrid-deployment/set-up-office-365-groups

       

      Kind Regards
      Oliwer sjöberg

      • AtanasM's avatar
        AtanasM
        Iron Contributor
        Apr 23, 2020

        Hello oliwer_sundgren 

        The groups write back is already activated.
        However, this has no influence on the access to the calendar from Teams and it is still not visible.
        The Teams client tries to connect to the local Exchange but gets a response error 400.
        This happens both in the WebClient and via the installed Teams client (verified with Fiddler).

         

        ErrorCode: ErrorNonExistentMailbox, ErrorMessage: Mailbox doesn't exist; StatusCode 400

         

        Please check the attachment.

    • ThomasStensitzki-MVP's avatar
      ThomasStensitzki-MVP
      MVP
      Apr 22, 2020

      AtanasM How is the on-premises Exchange Server published to the Internet? Is Windows Server 2016+ Application Proxy used, or another reverse proxy component?

      In regard to the Exchange hybrid configuration, is AutoDiscover DNS used or does the Exchange hybrid configuration use a static TargetAutodiscoverEpr?

      • AtanasM's avatar
        AtanasM
        Iron Contributor
        Apr 30, 2020

        ThomasStensitzki-MVP I added the local web service URLs as SPN in Azure AD and this solved the issue. For instructions, see the following link and section: “Add local web service URLs as SPNs in Azure AD”:

        https://docs.microsoft.com/en-us/office365/enterprise/configure-exchange-server-for-hybrid-modern-authentication 

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