Turn on Case Requests
You can turn on Case Requests which means that rather than being automatically added to a case, you now have to accept or decline each request to be added to a case
Note that Case Requests need to be turned on by each user who wants the option to accept or decline invitations to join a Case.
Steps
Turn on Case Requests by going to your Edit Settings page, navigating to the Email Notifications tab and ticking the “I must accept an invitation” tickbox
Press Save Settings
Related pages
Get Notified of an incoming invitation (request) to join someone else’s Case