app/views/layouts/mailer.html.erb
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html lang="<%= I18n.locale %>">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title><%= message.subject %></title>
<style>
body { font-family: "Helvetica Neue", Helvetica, Arial, sans-serif; font-size: 16px; line-height: 24px, color: #000000; }
@media only screen and (min-device-width: 541px) {
.content {
width: 540px !important;
}
}
</style>
</head>
<body>
<!--[if (gte mso 9)|(IE)]>
<table width="540" align="center" cellpadding="0" cellspacing="0" border="0">
<tr>
<td>
<![endif]-->
<table class="content" align="center" cellpadding="0" cellspacing="0" border="0" style="width: 100%; max-width: 540px;">
<tr>
<td>
<%= yield %>
</td>
</tr>
</table>
<!--[if (gte mso 9)|(IE)]>
</td>
</tr>
</table>
<![endif]-->
</body>
</html>