mailhtml.twig

<style type="text/css">
body {
    font-family: sans-serif;
}
ul {
    list-style: none;
    padding-left: 1em;
}
p {
    white-space: pre-line;
}
</style>
<h1>{{ subject }}</h1>

<p>{{ text }}</p>

{% for name, values in data %}
<h2>{{ name }}</h2>
<ul>
{% for value in values %}
    <li><pre>{{ value }}</pre></li>
{% endfor %}
</ul>

{% endfor %}