corrupted email attachments

The problem started about 6 weeks ago. The email Jpeg attachments I was sending were corrupted. Sending emails to myself verified the problem. My primary email program is ThunderBird, but I tried Outlook and Outlook Express with the same results. I also tried other formats (gif, tiff, etc..) with the same results. I tried Web Mail and it had no problem with attachments. I tried several virus programs .... they found no virus. My operating system is WindowsXP and all current updates are installed. What's wrong??

 

After significant trial and evaluation I have been able to determine my problem was caused by my Norton Virus program (part of Norton SystemWorks 2005). By disabiling the incoming and outgoing virus scan the problemwas solved. This also fixed a problem I had connecting to my mail server. The virus scans were randomly preventing that connection.