Stay organized with collections
Save and categorize content based on your preferences.
One of user is sent mail to all group without permission.
Remove the Member with the name All users in the organization in the Group Member's list via the Admin Console.
Admin Console > Directory > Groups > Group name > Members.
Hover mouse to the Member All users in the organization.
Hover over to the right and select Remove.
Even if a Superadmin cannot send emails to a Group since Permission access prevents them to do so, however since the Group Member "All users in the organization" is listed on the Group then all Users in the company can send emails to the Group.
All users are a member on the Group without them showing as individual Users.
It happens when a Superadmin/Group manager/Group owner does the following steps:
Admin Home > Directory > Groups > Group name > Members > Add members > Choose Advanced > select box 'Add all current and future users of Organization to this group with All Email setting' > click Add to Group.