"Love it or hate it, there’s no denying the popularity of HTML emails." The question should be with whom are they popular. I think people who get emails don't

"Love it or hate it, there’s no denying the popularity of HTML emails." The question should be with whom are they popular. I think people who get emails don't care if they are HTML or plain text. Text savvy people might be very opposed to HTML mails. The best way to achieve responsive design is to not use a design at all. Plain text especially with format=floated is responsive. If you use HTML, use only to highlight things you want to highlight and avoid huge graphics or graphics at all. The idea of using more then one column, which I have seen sometimes, is beyond weird for me.