GrowMore Mention User is a SuiteCRM add-on that sends a notification to any user when another user @-mentions him or her in a comment. The mentioned user will receive a CRM default notification, email notification, and browser desktop notification.
Go to the Accounts, Contacts or Leads module and find field Add Comment Description.
In that field you can type @ follow by username. And write any comment. That comment will be receive by username to whome we are mention.
Below screenshot for auto suggestion username of SuiteCRM.