format string email to email-link
<p>I have a nullable-string email, and I would like to format the string as a mailto-link if it seems valid.</p>

<p>like this:</p>

<pre><code>&lt;a href="mailto:foo@foo.com"&gt;foo@foo.com&lt;/a&gt;
</code></pre>

<p>How is that done?</p>

<p>/M</p>
