Users are noticing a bug that happens on Microsoft’s new Windows Phone 7 platform in regards to the email capabilities. When forwarding an email from a non-Exchange account, the forwarded email would get attached as an EML file rather than get appended inline as the body of the new forwarded email. Microsoft is now examining the issue, according to a company tweet.
The problem only occurs if you are not using an Exchange email, such as Google or Yahoo! Mail.
A circuitous work around for this solution would be to reply to the email, rather than forward it, and delete the pre-populated reply address field and fill it in with the email address that you would want to forward the email to instead.