If  you think your email messages stored on your computer are important,it might be worth back up  them on a regular basis to prevent them to be lost.
Here few easy steps to do the job:

1. Open Outlook Express
2. Click on Tools and select Option




3. On the next window click on Maintenance Tab and Store Folder




4. On the next window press Tab key until you see all the words in the Text box are being Highlighted




5. Right-click on it or press cntrl +  c to copy the text and
6. click start
7. Click Run
8. On the next window right-click in the box and select past,
   or press cntrl + v




9. Click Ok or press enter
10. Now you are in the folder where all your e-mails are stored.
    
    
    
11. Do whatever you normally are doing to back-up your files on a removable media like a cd or dvd.My personal suggestion is to use Nero back-up.