This was originally an OutlookExpress problem, then I tried
Thunderbird, and Outlook, and had the same problem.

I send an email from one of my two almost identical
computers and the email always arrives blank. When I check
the [Sent Items] folder the message is not blank. I tried
uninstalling my McCafee virus protection software, the
problem remained. I first tried uninstalling OutlookExpress
and then reinstalling it, same problem. Then I tried
Thunderbird, same problem. Then I bought a copy of Outlook
2002 on Ebay, and installed it same problem. All of the
emails from others arrive correctly. All of the emails that
I send (to myself or others) arrive completely blank, some
of the routing info remains, but all of the displayable
fields are blank.

What could be causing this? What can I do to fix it?