This setting chooses the message category that Classter assigns to the messages sent by the Notification Service. You configure the Notification Service itself with Configure Notification Services here, which sits directly above this setting in the same group.
The full article is available to signed-in Classter users.
Sign in with your Classter account — if you are already signed in to your Classter Portal you will not be asked for credentials.
Sign in with ClassterIntegration partners only — external partners without a Classter account.
Classter staff and customers: use Sign in with Classter above.
Partner sign-in with Microsoft