04-21-2020 07:22 AM
04-21-2020 07:22 AM
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.
The Calendar Sharing between On Premises and Cloud Users work.
The calendar is available in OWA.
All on prem users are affected.
Error message: "Your exchange calendar isn't set up. Talk to your admin to set up you calendar".
Exchange Server 2016 CU12
04-21-2020 09:47 AM
@AtanasM Did you check the external authentication methods on the AutoDiscover virtual directory?
It seems that Microsoft Teams cannot fetch AutoD version 2 data from your on-premises Exchange Servers. Are all Exchange virtual directories published to the Internet?
04-21-2020 11:36 AM
Tried enabling Group-Writeback?
Also make sure that OAuth is set up correct
04-22-2020 08:44 AMSolution
@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?
04-22-2020 11:45 PM
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
04-23-2020 06:48 AM
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.
04-23-2020 07:27 AM
Hello @AtanasM !
I see, the error message is strengthening the theory that @Thomas Stensitzki Had regarding Autodiscover.
The error message says that "Error while fetching apointments from EWS" And that the mailbox was not found.
So there seems more likely that Autodiscover is the issue here.
Is it possible for you to share your Autodiscover and EWS Virtual Directories configurations with us?
04-23-2020 07:47 AM
@Thomas Stensitzki The local exchange is addressed via a load balancer (KEMP Loadmaster). Inquiries to EWS etc. are passed on.
The HCW has filled out the TargetAutodiscoverEpr automatically.
from EXO to on premises and from on premises to EXO.
However, I have only tried it with registered target sharing EPR, but this did not lead to success.
04-23-2020 08:57 AM
@AtanasM I'd recommend the following steps for troubleshooting this further:
04-29-2020 11:07 PM
@Thomas Stensitzki 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”: