When you comment in a file and use the @-sign with someone's name, they receive an email with a link to your comment. Clicking the link brings them into the document and conversation.
Add a comment.
Type your comment. Use an @mention to name specific people in your comment.
Select Post comment.
The recipient will receive an email notification. They can reply to the comment right from the email or select the link to go directly to the comment.
Tip: When you @mention someone in the web, you can add a task to the comment to track work.
Insert or delete a comment in Word
Add and review comments in Excel
Insert comments and notes in Excel
Add, reply to, or delete comments in PowerPoint