How to make the notification settings enabled to all the users?

Hi All,
I am the Admin for my discourse site, now I want to make the ‘notification & email settings’ to enable by default.

Scenario 1: If I am creating a new topic under one category, I want to notify all the user by sending the email with created topic details.
Scenario 2: If I make one of the user as Moderator and he/she created a new topic under the category, I want to push he email notification for all the users.
Scenario 3: If I have created a group ‘XYZ’ with set of people and moderator has created the topic under one category, and it should push the email notification only to that group members.

How to achieve all these scenarios, Can someone help.

There is a variety of controls you can set for users ho jaye ng your site to watch, track topic category and or tags

Custom groups also have options for category & tags.

You can create (sub-)categories, in which you limit, who is allowed to create (and reply to) topics. So you only allow topic creation for those, who should be able to create a notification. And you limit “see” to those who should be able to receive the notification
Understanding groups and category permissions (security settings)
Then you change the default notification level for these categories to watching first post.
Configuring Default Notification Settings for Users