Microsoft Teams Support when user mailbox is in Exchange On-Premises

I have been asked a lot lately, it is possible to use Microsoft Teams while still having your mailbox located on Exchange On-Premises.

The answer is yes, this is a supported scenario.  Microsoft Teams has a strong dependency on Exchange Online because all of your personal discusses are stored in Exchange Online.  If the user’s mailbox is still on-premises, a cloud-based storage area will be created for that user called a “cloud-based mailbox for on-premises user”.  This solution will only store Teams conversations and the user cannot directly log into this mailbox.

To support this, you must have Exchange Hybrid configured and you must be using AAD Sync.
To enable this, there is a request process you must go through, defined in the references below.

Additionally, if the on-prem mailbox is ever migrated to Exchange Online later, the Teams chat data will not be lost, the data will be migrated over to the primary mailbox in the cloud.

https://docs.microsoft.com/en-us/MicrosoftTeams/exchange-teams-interact
https://docs.microsoft.com/en-us/office365/securitycompliance/search-cloud-based-mailboxes-for-on-premises-users