Why HTML email is BAD

Click here for a full size screenshotThe screenshot above is an email spotted today in my spam box. It's a conventional phishing email with a classic call-to-action and a link whose URL takes victims to the phishing site rather than CitiBusiness.
What caught my eye, though, was the hex encoded gibberish at the bottom. I can't be bothered to convert it all to readable characters and probably don't have the skills necessary analyze it and figure out exactly what it's doing but the few unencoded words (api, update, end, exe, create, engine, close, define, revision, tmp, hex, URAW, rev., create, root:, LHY, serv, 22MP., source:, Y1TM, cvs, revision, 60T, 376T:) do rather give the game away: it looks like some sort of attempt to get victims' email software to execute code. My bet is that it exploits a bug in the way HTML emails are handled. Needless to say, my machine is configured to read emails as plaintext. I can live without the fancy text formatting, and malware, thank you very much.