Is 7.x support mime-email or html mail module ?

This seems to work for me to conditionally set it for emails containing HTML.

/**
 * Implement hook_mail_alter().
 */
function my_module_mail_alter(&$message) {
  //test if message body contains html tags
  if (preg_match('/<[^>]*>/', $message['params']['message'])) {
    // Set the content type to HTML
    $message['headers']['Content-Type'] = 'text/html';
  }
}