app/views/mailing/sender/notification.html.erb
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
</head>
<body style="margin: 0">
<%= raw word_wrap(@message) %>
<p>
--<br/>
<%= @signature_message %><br/>
<%= @url %>
</p>
</body>
</html>