Overview:
We need to enhance the sorting capabilities in Proton Mail to better support users managing multiple email addresses. The goal is to introduce an Outlook-style "Group by Category" sorting feature to improve inbox navigation.

Customizable Category Grouping (Outlook-Style)

Functionality: Within these folders, users need a customizable category display similar to the Outlook desktop app.

Sorting Logic: When an email is assigned a category, the user should be able to sort the folder by these categories.

Primary Sort: Group emails by Category.

Secondary Sort: Within each category block, emails must be sorted chronologically.

UI/UX Behavior (Collapsible/Top-Level Display): When the "Sort by Category" view is active, the categories should act as collapsible headers. At a glance (or when collapsed), the user should see the categories listed right at the top of the folder. This ensures the user does not have to scroll down past all the folders and hundreds of emails in one category just to reach the next one.

Implementation: * This grouped view should be an optional toggle integrated directly into the existing "Sort" dropdown menu (e.g., a "Group by Category" option).

The standard, continuous scrolling view must still be available for users who prefer the legacy layout.