Saved search folders/smart folders
Save common searches as a virtual Search Folder
Create folders individuals, attachments, status, date and more
Folders can be defined by multiple attributes (eg individual + attachment + unread)
Like normal Folders, they can be moved and grouped within other inbox folders
Quickly define highly refined searches with Search Language or Visual Search Builder
Tim Klauck commented
It would be important to search for flagged messages and keep them permanently in a "Flagged" smart folder.