Typical boilerplate email response letters using plain text vs HTML email response using brochure type format, they even respond better to the generic HTML than to the customized plain text email.
These are emails to people posting job work available on any site, or "friends of customers wondering what we've done".
These brochures are based off email list type designs, such as would be used to solicit donations for a charity or to keep past customers informed of happenings at a retail outlet.
I'm not quite sure in what kind of context and what kind of audience: is it for contract/freelance kind of jobs to present yourself? (or your company)
Your comment made me wonder how that would work for full-time job applications and at first thought, I'd think it would annoy people more than anything because you'd be more likely to send them to your peers. (and the HN-type tend IMO to prefer plain text)
But, I'm ready to challenge that idea. If people have used HTML emails for job applications/cover letters with success, I'd be very interested to read about it because it sounds like it's not the right place to do so, but it would still make one pop out of the pile.