<head>

This tag can contain the title of the document, scripts (banned in emailing), styles, meta information… <title>, <style>, <meta>, <link>: This data can be specified directly in the <head> tag of the document. It's a structural element, just like <html> or <body> tags.

<!DOCTYPE HTML>
<html lang="en">
<head>
<!-- content -->
      </head>
<body>
</body>
</html>

Inside the <head> tag, the media queries for the responsive version of an email will be written.

<!DOCTYPE HTML>
<html lang="en">
<head>
<style>
<!-- beginning of media queries -->
      @media screen and (max-width:600px) {
    .container-table {}
}
<!-- end of media queries -->
      </style>
</head>
<body>
</body>
</html>

A question?