在电子邮件golang中未翻译html

I'm actually trying to send email with html content with golang and net/smtp lib. But when i send email, html is not translated and i receive an email like that :

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
        "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html>

</head>

<body> <p>
    Hello Louis
    <a href="http://google.com/">Confirm email address</a> </p>

</body>

</html>

Because with my own code it did not work, i've tried with this tutorial but it doesn't work either..

So with the example of this tutorial why i receive email in the form of string and not in formatted html ?

ps : My code is absolutely the same as in the tutorial

That sample is wrong. On line 46, it has

mime := "MIME-version: 1.0;
Content-Type: text/plain; charset=\"UTF-8\";

"

Namely the Content-Type: text/plain). If you're sending HTML mail, you should use Content-Type: text/html.