Update 12/15/2025: We modified the date of this change to end of June 2026 based on customer feedback. Please use that extra time to remove your dependencies on EWS.
As part of our ongoing efforts ...
Updated Dec 18, 2025
Version 4.0
Blog Post
Hello,
In Hybrid environments, for accounts where mailboxes are hosted on On-premise Exchange and which only use Teams on the M365 side (with a package like Microsoft Teams Essentials etc.), I believe the Exchange-Teams calendar synchronizations and Free/Busy availability status should not be affected by this EWS restriction, but I am not entirely sure about this. What do you think?
MS Teams has a 2GB mailbox in the background to process objects like the calendar, etc. This mailbox is not visible in Exchange Online, cannot be used directly as an email account by people, but it still exists; it must exist. As far as I know, this mailbox package does not have a plan equivalent (like F1, F3, Kiosk, Plan1/2 etc.). Microsoft explicitly defines this mailbox used by Teams as 'Teams uses a lightweight unlicensed Exchange mailbox for Calendar.'
Note: Microsoft says "that standalone Teams packages do not include Exchange Online". However, I once observed that due to an issue locally, the Exchange server was freshly installed, the Hybrid structure was broken during this process, and 2GB mailboxes were created for the users in Exchange Online.