Use plain-text email
"[Plain-text email] is strongly preferred"I think it's significant that this is written in the passive voice. Because written this way it has the semblance of officialness, of generalness. Whereas writing it in the active voice would reveal that the people doing the preferring are just the people who made this website, and this preference is just that: a preference.I love HTML emails, because I use italics basically all the time in my writing, and underscores _just don't offer the same experience_.