Re: Sigh. Not again.
We need a new protocol, because email has been breaking for a long time now and this looks like the last straw.
This isn't email breaking, this is an inherent problem with HTML.
As with so many email-related risks, reading in plain text by default obviates this issue. If switching to HTML requires a positive action, the user should already be warned that strangeness might be around the next corner.
But most people seem far more interested in shiny shiny than in security...