Teams uses EWS-API wrong which leads to wrong timezone in meetings

Copper Contributor



we do have an Exchange Hybrid Setup. On-Prem we do use OWA only. No Outlook-Client.


When a user creates a Teams meeting (inside the Teams calendar) they sometimes use OWA when changing the meeting for comfort reasons (drag&drop). Here the problems begin.


A little example:

- User sets up meeting at 11:00 a.m. within the Teams calendar.

- User changes meeting to 9:00 a.m. via OWA on the Exchange on-prem

- Within in the organisation, everything is OK. But every External now has the appointment at 1:00 p.m.


So somehow Exchange does a +2h (summertime maybe involved) to the orginal starting time of the meeting. But just for external participants. Inside the organisation everything is fine. Exchange always does the +2h based from the original meeting starttime. So moving the appointment to 3:00 p.m. will also lead to 1 p.m. for the External.


Technically the .ics gets changed from "W. Europe Standard Time" to "UTC".


If we change the meeting in the Teams calendar, everything is fine. If you create the meeting On-Prem and change it On-Prem or in the Teams calendar, everything is fine. It is just Online created meetings, changed On-Prem what causes the issue.


I attached a screenshot of the .ics file. Right side shows the original meeting from Teams. Left side shows the changes of the meeting after leaving Exchange On-Prem.


Does anybody have an idea where to look?


Cheers Sebastian

3 Replies

Hi @Sebastian_Rottmann,


this looks like a bug in the MS construct itself.


I have no idea how to fix it. You should create a MS Support case.


Best regards,

"First, No system is safe. Second, Aim for the impossible. Third, no Backup, no Mercy" - Schnittlauch

My answer helped you? Don't forget to leave a like. Also mark the answer as solved when your problem is solved. :)


So after a while debbuging with MS support we still have no solution. But we know what's happening. Or we think we know. Who knows? :)

1. Meeting created in Teams (Teams Online, Web-Browser)

a) Teams-Online uses SMTP to send the meeting to the external user over our hybrid environment (mail-flow). The meeting shows itself correct inside the external calender, because the meeting uses UTC+1 or Western Europe Standard (CET). The meeting isnt "changed" in anyway over the SMTP-flow.

b) Teams-Online uses EWS to write the meeting into the local users calender. The meeting shows itself correct, because the OWS-settings of the user are configured to UTC+1. But the meeting itself is created "incorrect". That leads to the bug we see.

Teams-Online puts the meeting with UTC to the EWS-API, although the user created it with UTC+1. We think that's the problem.

2. Changing the meeting with OWA in Exchange On-Premise

The meeting is internaly saved as UTC. See 1.b) Updating the meeting sends an update to the external user. The base is UTC, instead of UTC+1. So we have a missmatch for the external user. The internal user still sees the meeting correct, because their local enviroment is set to UTC+1.

So does anybody know if there is a setting for the timezone?? somewhere teams ignores the correct timezone, when adressing the EWS-API? The user-settings (, using Teams-Online are set to UTC+1. The meeting is created with UTC+1 within Teams-Online. We looked at the clients timezone-settings. Those we also set to UTC+1/CET. But EWS uses UTC. 

Can some look how their meetings are created through EWS using the Web-Client of Teams. Using the Teams-App on iOS shows the same problem. It should be something between the "Cloud" and our "Hybrid" environment.

Attached you find a screenshot of the EWS-debugger. You see a meeting created by Teams-Online for 14:30 (UTC+1) written through EWS to Exchange On-Premise.

"So after a while debbuging with MS support we still have no solution. But we know what's happening. Or we think we know. Who knows? :)"
MS at it's best ;)

Offtopic/fun: reminds me of the following meme: