Several users in your organization have the "Monitor Cases" Support Site role. This role

Allows the user to receive email notifications whenever an update is made on any support case opened for their organization or one of their customers' organizations. This role is not necessary to monitor cases the user opened themself, and may result in a high volume of notifications.

For users who do not want an email notification for every update made to every support case, you can just remove that role for those users.