MS Outlook XP – Personal Folder

The size of my personal folder keep growing to close to 800MB. I have tried to delete as much unwanted mail and clear the empty folder but its size did not reduce. Why is that so?

I have even tried to delete all the mails but the size is still as big. When I try to import this personal folder file to a new profile, it is empty. Why is it empty when the file size is so big?