Currently in Comms, when you mention a user they are automatically added as a recipient of the message. You can, however, choose to manually remove that recipient. In this case, it’s possible for a user to be mentioned but not receive a notification for the message—which is currently working as intended (though @John Carroll doesn’t like this “feature”). However, if you mention someone in a draft, then remove them as a recipient, then close the draft, then open the draft again, the mentioned person will automatically be added back as a recipient.