Microsoft Teams: specifications and possibilities of the shared channels

I'm definitely saying that the documentation is incorrect. It's the latest in a long line of incorrect statements on this topic. Never believe what you read in documentation until you verify it for yourself.

The facts are that the Microsoft 365 substrate captures compliance records for Teams messaging and stores them in EXO mailboxes.

• User mailboxes for personal chats and private channel conversations.
• Group mailboxes for regular channel conversations.
• Cloud-only special mailboxes for shared channel conversations.

Cloud-only mailboxes are also used to capture contributions by hybrid and guest users and for external federated chat. 

The compliance records generated by the substrate are mail items customized to meet the needs of eDiscovery and other compliance solutions: https://office365itpros.com/2020/12/22/teams-compliance-records-ediscovery/. They are incomplete copies of the actual messages. For instance, they don't capture reactions to messages or voice messages. Reactions have only lately started to be captured in audit records: https://office365itpros.com/2022/09/08/teams-reactions-captured-audit/