Exchange On premise Calendar integration with MS teams

The existing answer correctly identifies Autodiscover, EWS, and OAuth as the main requirements. Here is a more practical configuration checklist for Teams Calendar with Exchange Server on-premises.

1. Verify that users are synchronized to Microsoft Entra ID through Entra Connect Sync, with the Exchange Hybrid Deployment option enabled.
2. Confirm that users with on-premises mailboxes are represented as MailUser objects in Exchange Online, rather than Exchange Online mailboxes.
3. Make sure the published Autodiscover V2 and EWS endpoints are accessible from the required Microsoft 365 services over HTTPS. Reverse proxies or firewalls must not block the required requests.
4. Verify OAuth configuration, including the EvoSTS AuthServer in Exchange Server.
5. Check that the published Exchange HTTPS namespaces are registered as Service Principal Names (SPNs) on the Exchange Online service principal in Microsoft Entra ID.
6. Run the Teams Calendar App test in Microsoft Remote Connectivity Analyzer. Once successful, verify calendar visibility and event synchronization between Teams and Outlook.

The Hybrid Configuration Wizard is the preferred approach for configuring OAuth, but it is not strictly required. Microsoft also documents manual OAuth configuration.

I configured Teams Calendar manually with Exchange Server SE, without running HCW. I also configured Teams Meeting Delegation separately.

The article explains the components, PowerShell commands, configuration steps, and verification:

Exchange Server and Teams Calendar Integration Without HCW

Hi @GoodResource

Have you checked this link?
Configuring Teams calendar access for Exchange on-premises mailboxes

Please refer to this part:

To make calendar access work for your on-prem mailboxes, Teams needs access to your Exchange on-prem organization for both Autodiscover and EWS. There are several things to remember here.

• Autodiscover and EWS URLs should be available from the Internet. Pre-Auth is not supported. If you use some sort of publishing system, you will need to configure pass-through. You can verify that external URLs on-prem are accessible, trying to open them from internet directly in web browser. Test with https://mail.contoso.com/EWS/Exchange.asmx and https://autodiscover.contoso.com/Autodiscover/Autodiscover.xml .You can also use http://aka.ms/exrca to test connectivity for EWS and AutoDiscover. But note, that those tests don’t use OAUTH (as of this writing). So, sometimes you might see that those tests pass successfully, but free/busy for on-prem users is not visible from your tenant (see further below for more troubleshooting tips).
• OAUTH authentication should be configured and working between you O365 tenant and Exchange on-prem. To make this work, we highly recommended to run Hybrid Configuration Wizard (HCW) to configure full hybrid mode. For on-premises deployments (newer than Exchange 2010) HCW automatically configures OAUTH between on-premises and EXO. Please make sure to run the latest CUs on-premises as per our Hybrid requirements.

The article also includes troubleshooting methods, which may help when it is still not working for you after the configuration.

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