Over the last several months, we have seen many customers adopting Microsoft Teams, even if their mailboxes are still hosted in an on-premises environment. One of the common issues in this scenario i...
Updated Nov 09, 2023
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Blog Post
PeterRising - the second article linked shows that EX2013 mailboxes are supported for the delegate access. Seems like the requirement is around AutoDiscover v2 support:
https://docs.microsoft.com/en-us/microsoftteams/exchange-teams-interact
Teams Scheduling add-in for Outlook when scheduling a meeting on behalf of someone requires Exchange 2013 CU19 or later. This is to support the unauthenticated discovery of the mailbox by our service to check delegate permissions against the delegator mailbox. The delegate and delegator location could be Exchange 2013 or later, or Exchange online, but Autodiscover must resolve to Exchange 2013 CU19 or later
Trying to test in the lab.