<head> so you would also have to use inline CSS.
That pretty much precludes the use of media queries, which for me is the final nail in the coffin of a responsive e-mail design.
Chris covered some of these pitfalls in a post back in 2007 ( https://css-tricks.com/using-css-in-html-emails-the-real-story/ ) and you can read a more recent article on the MailChimp knowledge database ( http://kb.mailchimp.com/campaigns/ways-to-build/css-in-html-email )
The TLDR of it all… many of us still use
<table> for e-mail structure because it’s a better solution than the insane amount of inline CSS you’d have to apply while still hoping E-Mail Service X didn’t strip it all out anyway.