In some cases it may be undesirable for users to mention other teammates, thereby inviting them to the conversation. Some examples
Users should only be able to mention other teammates with access to the current Workspace
Users should only be able to mention other teammates with access to the current Inbox
Preventing a team of users being mentioned directly (e.g. developers) so that they can control how they manage internal requests for help
Really need this to help prevent users from @ mentioning external users and accidentially exposing internal comment threads that shouldn't be shared outside the company.