Sorting mail
You can change the order in which messages are displayed in a given folder. This is only valid in list view and preview-below view.
To sort messages
You can order the messages in the mail view in the following ways:
- Click on the column heading.
The current column that is being sorted is indicated by the sorting icon. 
for descending and 
for ascending.
From can be sorted in alphabetical order( a-z or z-a).
Priority can be sorted in priority order ( high-low or low-high).
Subject can be sorted in alphabetical order (a-z or z-a).
Date can be sorted ascending or descending date order.
Size can be sorted in ascending or descending order.