M365 Outlook - Using @mentions
@mentions is a feature in Outlook on the Web that you can use to get someone's attention or use to find mails that mentioned you. @mentions will be available for Outlook 2016 for Windows and Mac, Outlook for iOS, Android and Windows 10 Mobile in the fourth quarter of 2016.
To use @mentions to get someones attention, type the @ symbol into the body of your email and start typing the name of the person you would like to address. Click on their name to confirm the person, once the person is picked, their name will be highlighted in blue. If the person you mentioned wasn't originally in the email's To.. box, mentioning them will automatically add them to ensure they receive a copy of the email.
Note: You can also delete a portion of the mention, such as the last name. So @Wendy Richardson can be @Wendy
Searching for messages that mention you
In addition to getting someone's attention using @mentions, you can also use it to be aware of messages you have been mentioned in. You can quickly glance what emails you have been mentioned in by seeing if there is a @ symbol in the in the message.
To filter the message list to display only emails in which you were mentioned, simply switch the message filter to Mentions