All logged in users are able to mention others users, This functionality is implemented for:
Posts (In groups, on profiles or in the community)
Comments (on Topics, Events)
Start typing an @ followed by the name or username of the person you want to mention; a list of (max 8) results will appear.
The user who has been mentioned, will receive an e-mail and personal notification.
When being mentioned in a comment, you will also receive notifications of replies to that comment.
Mentions are also used to reply on a reply.
Manage e-mail notifications settings in your account!