Pear Mail, how to send plain/text + text/html in UTF-8

I'm trying to send an email in both text and html, but I can't correctly send the right headers. In particular, I'd like to set the Content-Type header, but I can't find how to set it separately for html and text parts.

This is my code:

$headers = array(
  'From'          => '[email protected]',
  'Return-Path'   => '[email protected]',
  'Subject'       => 'mysubject',
  'text_encoding' => '7bit',
  'text_charset'  => 'UTF-8',
  'html_charset'  => 'UTF-8',
  'head_charset'  => 'UTF-8',
  'Content-Type'  => 'text/html; charset=UTF-8'
);

$mime = new Mail_mime();

$html = '<html><body><b>my body</b></body></html>';
$text = 'my body';

$mime->setTXTBody($text);
$mime->setHTMLBody($html);

$body = $mime->get();
$headers = $mime->headers($headers);
$mail_object =& Mail::factory('smtp', $GLOBALS['pear_mail_config']);
$mail_object->send('[email protected]', $headers, $body);

That's the email I get:

From: [email protected]
Subject: mysubject
text_encoding: 7bit
text_charset: UTF-8
html_charset: UTF-8
head_charset: UTF-8
Content-Type: multipart/alternative;
    boundary="=_7adf2d854b1ad792c802a9db31084520"
Message-Id: <.....cut.....>
Date: Mon,  8 Oct 2012 15:40:54 +0200 (CEST)
To: undisclosed-recipients:;

--=_7adf2d854b1ad792c802a9db31084520
Content-Transfer-Encoding: 7bit
Content-Type: text/plain; charset="ISO-8859-1"

my body

--=_7adf2d854b1ad792c802a9db31084520
Content-Transfer-Encoding: quoted-printable
Content-Type: text/html; charset="ISO-8859-1"

<html><body><b>my body</b></body></html>
--=_7adf2d854b1ad792c802a9db31084520--

It seems that the Content-Type header I set is totally ignored. I'd have expected some setHTMLHeaders and setTXTHeaders functions, but it seems like there's nothing like this. Am I missing something? How can I set both Content-Type headers to UTF-8?

Solution

I discovered that the headers are supposed to be written differently. In particular, some of them are parameters for the mime object, and not email headers. Then the mime_params array should be passed to the get() function.

This is the correct way to set the headers:

$headers = array(
  'From'          => '[email protected]',
  'Return-Path'   => '[email protected]',
  'Subject'       => 'mysubject',
  'Content-Type'  => 'text/html; charset=UTF-8'
);

$mime_params = array(
  'text_encoding' => '7bit',
  'text_charset'  => 'UTF-8',
  'html_charset'  => 'UTF-8',
  'head_charset'  => 'UTF-8'
);

$mime = new Mail_mime();

$html = '<html><body><b>my body</b></body></html>';
$text = 'my body';

$mime->setTXTBody($text);
$mime->setHTMLBody($html);

$body = $mime->get($mime_params);
$headers = $mime->headers($headers);
$mail_object =& Mail::factory('smtp', $GLOBALS['pear_mail_config']);
$mail_object->send('[email protected]', $headers, $body);