What is @Mentions?
When you type @ in the message body and begin typing a name, an autocomplete list pops up. After you select the name of the person, if the person is not on the conversation, their address is added to the To field. The @mentions in the message body is highlighted for better visibility.
Why would you use it?
To get someone’s attention and point out that you are asking them to do something mentioned in the message.
When @mentions is enabled, a new filter, Mentions, appears next to the All and Unread filters at the top of the message list. This displays a list of messages you were @mentioned in, so you can easily find the messages that need your action.
When a message arrives with a mention in it, the message list will display an @ symbol next to the message and in the thread’s group header.
When you send an email and type @ in the message, you can select a name to use in the @Mention. If you aren’t typing a mention, keep typing and the autocomplete list will disappear once you run out of matches and enter a space. If the dialog won’t go away after displaying the message “We couldn’t find the person you were looking for.”, press ESC to dismiss it.
When the message is sent, the @mentions are in the message body.