Mentions
Channels (users) are labelled by simply prefixing their name (handle) with the @ sign. @Jack
When you mention someone, an autocomplete field is created from which you can select your immediate connections. Select accordingly.
If the contact is authorised to receive your posting, they will receive a tag notification.
If the addressee is not in your contact list, you must write out the handle after the ‘@’ sign. If the recipient also authorises mentions of third parties, they will also be notified of the mention.