Office Outlook Web Access injects unwanted CSS in our emails. What triggers this and how to fix it?

Question

The injected styles result in all text being underlined. It does not inject the styles in messages originating from Outlook, and does not inject them in all HTML-formatted messages.

Our HTML templates show properly in all clients including the Outlook native client and Hotmail which supposedly uses a similar HTML email preprocessing to the one deployed by Outlook WebAccess ( http://litmus.com/help/email-clients/rendering-engines )

I am wondering what exact issue triggers this behavior. Is there a way to prevent the injection by modifying my HTML emails? Here's the CSS it injects:

Edit: I just noticed it does it for all browsers except for IE.

<style type="text/css">
<!--
.x_preheaderContent 
  {color:#606060!important;
  font-weight:normal!important;
  text-decoration:underline!important}
.x_headerContent 
  {color:#EB4102!important;
  font-weight:normal!important;
  text-decoration:underline!important}
.x_bodyContent 
  {color:#0000cc!important;
  font-weight:normal!important;
  text-decoration:underline!important}
.x_footerContent 
  {color:#000099!important;
  font-weight:normal!important;
  text-decoration:underline!important}
-->
</style>

Answer 1

It looks to me that code is an interpretation of what Outlook understands of style and how it is applying. You have most probably taken the above code by viewing the source of the html email from the Outlook. If you look at your html code and then setting or overriding the text underline property should be as smooth as anything else. I never had issues with this property.