What is it?
Group By is a feature that allows you to group the items in the active folder based on the following parameters:
None
Type
Importance
Action
Attachment
From
To
Subject
Sent Date
Received Date
Target Date
Tag Date
Size
What happens if clicked?
A submenu appears that allows you to define how you want to present the items in the active folder.
You can decide not to apply any Grouping by selecting None at the submenu.