When a user is activated
Sends a notification when a User account becomes active. The trigger fires whenever Craft transitions a User into the active status. Most commonly that happens when the User clicks an email verification link, when an administrator activates a pending account, or when an admin re-enables a previously suspended User.
User Group Filters
Choose which user groups should fire this notification. Only users belonging to one of the selected groups will trigger it, and a user in multiple selected groups still receives only a single notification.
Ungrouped Users are users who belong to no group at all.

Selection is required
Check at least one group (or Ungrouped), or the notification won't fire.
Hidden if no groups exist
If no user groups are set up, this filter is skipped and every valid user will receive the notification.
Field Conditions
Field conditions restrict the notification based on the element's content, using Craft's native conditions framework. Build a rule set against the element's attributes and field values, and the notification will be sent only when every rule matches.
Must match all conditions
The condition builder evaluates every rule with AND semantics, so each rule must pass for the notification to be sent.

Twig variables
The object variable (and its user alias) is the activated User.
{{ user.fullName }}'s account is now active.Caveats
Activation, not registration
A new User is not necessarily activated the moment they register, their status may be set to pending. If your site requires email verification, this notification will be sent after they click the verification link.
To send a message at registration instead, use "When a new user is created".
Examples
Welcome the activated user
Hi {{ user.firstName }},
Your account is now active. You can log in any time at {{ siteUrl }}.Alert administrators of an activation
{{ user.fullName }} ({{ user.email }}) has activated their account.Skip when the user is in a specific group
{% if user.isInGroup('imported') %}
{% skipMessage "Imported users do not receive activation emails." %}
{% endif %}