This is a new feature introduced in Moxtra version 5.0. This is the section where all the message posted to you, to-dos assigned to you by other team members will be shown here. This section also shows the chat messages that you have marked as favourite from all the Binders or Group Conversations.
To view all the chat messages posted to you, just click on Mentions and you'll have all the chat messages posted to you by different team members from different Binders and Group Conversations here
To view all the chat messages marked as Favourites by yourself, just click on Bookmarks, and all the chat messages and files favourited by yourself will appear here
To view all the to-dos assigned to you by yourself and other team members from different Binders and Group Conversations, just click on To-Dos