Additional chat-related features and issues within Microsoft Teams for business
Partly correct.
The Guest access > Messaging > Chat setting controls whether guests can use chat in Teams at all. If it is On, guests can use chat. If it is Off, guests can't use chat.
The context supports that guests can participate in private chat when guest chat is allowed. It does not state that turning Chat on prevents guests from starting private chats or searching for other users.
What is supported:
- In the Teams admin center, Users > Guest access, the Chat toggle gives guests the ability to use chat in Teams.
- Guests can participate in a private chat.
- Teams admins control which guest features are available.
So the supported conclusion is:
- Chat = On: guests can use chat, including private chat participation.
- Chat = Off: guests can't use chat.
- The provided context does not confirm that this setting specifically blocks guests from starting private chats or searching for users.