to increase deliverability, we recently added a DKIM Signature to the emails. That is the only thing that has changed recently. we tested the emails with multiple email clients including Outlook 2010 without an issue.
is what you pasted above what shows in the body? or is that what you see when viewing the message source?
Not sure why it would work in Out look 2010 but not 2003, we can look into the problem with you if you like. If you provide a phone number or skype address we can contact you to try to find the cause.