As you know when on a Teams meeting participants can use the chat feature to communicate with each others.
You may be also aware that you can also allow anonymous or unauthenticated users to join a Teams meeting (if your Teams administrators allow it from the Meetings\Meeting Policies blade).
When combined together (chat feature and anonymous access) it may lead to potential data exfiltration.
Well, you can now disable write access to chat for anonymous or unauthenticated users from the same Meeting Policies blade.
To disable it, connect to your Teams administration portal (https://admin.teams.microsoft.com/) and access the Meetings\Meeting Policies to edit the policies you want to get it disable using the Chat in meetings option under Participants & Guests section by setting it to Turn it on for everyone but anonymous users
You can also use PowerShell – when you have install the Teams PowerShell modules available here https://www.powershellgallery.com/packages/MicrosoftTeams/4.5.0) using the command
Connect-MicrosoftTeams
Set-CsTeamsMeetingPolicy –Identity <meeting policy identity> -MeetingChatEnabledType EnabledExceptAnonymous
The accepted values for MeetingChatEnableType are:
- Enabled
- Disabled
- EnabledExceptAnonymous