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sandiven1154's avatar
sandiven1154
Copper Contributor
Jan 15, 2026

Teams calendar for exchange on prem users not working

Hello 
I am having issues to make  Exchange On prem users use  Calendar on teams.
Initially Client autodiscover was blocked externally but they added a cname and open flows but I am still having issues to makecalendar on teams work
HCW as passed and new hybrid dedicated app was used 

any help is welcome

 

exchange online
Exchange Server
hybrid
teams

3 Replies

  • ceyhunkirmizitas's avatar
    ceyhunkirmizitas
    MCT
    Oct 10, 2026

    Since HCW completed and you're using the dedicated hybrid application, I wouldn't start by running HCW again or recreating the OAuth configuration.

    I'd first run the Teams Calendar App test in Microsoft Remote Connectivity Analyzer. It should help narrow down whether Teams is failing at mailbox discovery, authentication, or EWS access.

    One thing worth checking is whether the affected on-premises mailbox users appear as MailUser objects in Exchange Online, with the correct on-premises mailbox information. Also verify the Exchange HTTPS namespaces registered as SPNs on the Exchange Online service principal in Entra ID.

    I recently configured Teams Calendar manually on Exchange Server SE and documented the individual OAuth and SPN components here: https://ceyhunkirmizitas.net/exchange-server-teams-calendar-integration-without-hcw/

    Your environment already has HCW and a dedicated hybrid app, so I wouldn't copy the manual configuration directly. I'd use the component checks to identify what's missing.

    The individual RCA subtest results would be particularly useful before making further changes.

  • NeonKnight's avatar
    NeonKnight
    Copper Contributor
    Jan 22, 2026

    Do you have firewall rules in place to allow the Teams cloud endpoints to talk inbound to your Exchange server? That was the final "gotcha" for me when I was setting it up. Spent 5 days reviewing configs trying to find an error or a missed step to realize I never requested the firewall team to open up the required ports.

  • Scott_Schnoll's avatar
    Scott_Schnoll
    MVP
    Jan 16, 2026

    For Teams to show calendars, the user must have an Exchange Online mailbox or be in a properly configured Exchange Hybrid with OAuth / Modern Auth working.  Is that the configuration you're using?

    You can do a quick test to see if things are configured correctly by running the following command (replace the placeholder user with your own user account):

    Test-OAuthConnectivity -Service EWS -TargetUri https://outlook.office365.com/EWS/Exchange.asmx -Mailbox email address removed for privacy reasons