Forum Discussion

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 is...
exchange online
Exchange Server
hybrid
teams
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.