Preface: I've only switched away from pine as my personal email client relatively recently... The vast majority of messages from actual humans in my inbox are

Preface: I've only switched away from pine as my personal email client relatively recently... The vast majority of messages from actual humans in my inbox are composed in plain-text. That doesn't mean it's sent to me in plain text, of course, but as far as the user is concerned they're typing in plain text without marking it up. The major culprit of fancy HTML shenanigans in this type of email is business-card like signatures (totally unnecessary). Messages which are intentionally formatted in HTML in order to display elaborate things come almost entirely (I'd say 99%) from websites (travelocity, evite), corporate newsletters, spammers, credit-card companies, etc. If those senders were restricted to plain text, those emails would most likely have less crap and more content which is pertinent to me. You don't need complex formatting to let me know my flight information, the my statement is available, or that my password has been successfully reset. Standardized formatting is important... I'm not saying that we should be restricted to a plan-text only world of email. But formatting restrictions aren't necessarily a bad thing (for extreme example, see Twitter). Just as email doesn't function well as a medium for sending large attachments, it similarly shouldn't be conceived of as a medium for displaying complex, elaborately formatted documents. That's what web browsers, word processors, and spreadsheet programs are for. Markdown, Basic HTML (1.0), or similar concepts are more than enough to convey your message clearly and directly, while allowing composers to organize their thoughts and link/include non-text information.