one of the application those people using, maybe yahoo webmail or word...

This is what I see when using mailwasher:

<html xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns="http://www.w3.org/TR/REC-html40">

That text didn't show up on yahoo webmail and Outlook express (with full header / properties details view)