1. All messages you send
   
2. Messages when someone mentions you by @name
   
3. Comments when someone mentions you by @name
   

Notes:

1. Messages cannot be deleted. Messages will always display on 1) on the page you sent the message and 2) in your Inbox.
   
2. Unlike messages, comments can be deleted. When a comment is deleted, the record is removed from 1) the section where you left the comment and 2) your Inbox. 
   

Here is an overview of the design and buttons inside your Inbox:

1. Archive icon: click to move a message/comment move to the Archived tab
2. Blue line: indicates a message that is unread
3. Project name will be displayed and formatted as a blue tag/label.
   Click the arrow above project name to open a separate tab with the document, section, or project
4. Circles and initials/profile picture: indicate all people in the message thread

Lastly, you can manage your Inbox over time by using your the Filter and Search tools.

See more about communication tools and notifications in this support article.