Why does this properly formatted html mail becomes garbled text when forwarded?

Question

I'm using Swiftmailer to send the contents of a form to a gmail account. The text appears as good html when first received but it turns into a garbled mix of html code and form contents when forwarded. Why is this? How can it be solved?

The message is something like:

$cuerpo_de_mensaje = "<h1>Resultado de Evaluaci&oacute;n de Curso ". $curso_tomado."</h1>".
                     "<h3>"."Participante"."</h3>".
                     "<p>"."El participante que llen&oacute; la evaluaci&oacute;n fue:&nbsp;"."<b>".$nombre_apellido."</b>"."</p>";

And it's sent using:

 $message->setBody( $cuerpo_de_mensaje, 'text/html');

Maybe it's this 'text/html' parameter the issue?

Answer 1

Changing the forwarding parameter to unicode utf-8 solved the issue.