Drupal7.x send HTML email

<?php
function mymodule_mail_alter(&$message) {
 
// if ($message['id'] == 'modulename_messagekey') {

 
if ($message['id'] == 'mymodule_messageKey') {
   
$message['headers']['MIME-Version'] = '1.0';
   
$message['headers']['Content-Type'] = 'text/html; charset=UTF-8; format=flowed';
  }
}
?>

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