app/views/user_mailer/welcome_new_user.html.erb
<html>
<head>
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type" />
</head>
<body>
<p>Welcome to <%= Rails.application.config.app_name %>!</p>
<p><%= link_to Rails.application.config.app_name, root_url %></p>
<p><strong>PLEASE DO NOT REPLY TO THIS MESSAGE</strong></p>
</body>
</html>