Notification by Mail sent even if option not activated


I have a problem with the notifications.
After installing NextCloud on linux server, features Notifications and Update Notification have been activated.
Then, when a user share a file, the user target receives a notification and a mail.
And after activating the feature Activity and desactivating the notification by mail, the user target continues to receive mail after sharing files !
What did i wrong ?
Can you explain me how works/differences the following features :

  • notifications
  • update notification
  • activity
    Thanks by advance.