Adding the size field to a folder

1. Make sure you’re in your Inbox (or any other folder)
2. Right-click on the Field Column Header - 
3. Select Field Chooser
4. Drag the Field called Sent to the Field Column Header
5. You can now sort your files by size as well as the other field headers.
6. Be sure to switch your sort back to Received  so you don't miss new mail.

Once you have created this column heading in the Information Window for any folder, you can sort on any column heading just by clicking on it.  This allows you to view your items in Size order so you can delete the largest items.

Be sure to click on the Received column heading when you are finished you so your items will be listed as you normally expect to see them.  Be aware that these column headings are toggles (click once on Received and they are listed with oldest messages on top; click again and they are listed with newest messages on top.