php mail sending problem. Server not accepting html tags

I developed a simple form with mai lsending function. When the file is in our server all the functionality worked greatly. But when the files moved to our client server, in mail sending we are facing some problem. What ever HTML code i used it's simply displaying in the same forma开发者_运维问答t. The HTML rendering is not happening properly.. Whether problem in the server or i have to change my php code??

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I believe you have setup the correct Content-Type: HTML on your email functionality. Please see: http://php.net/manual/en/function.mail.php#example-2881 for more information.

Quick Info:

// To send HTML mail, the Content-type header must be set
$headers  = 'MIME-Version: 1.0' . "\r\n";
$headers .= 'Content-type: text/html; charset=iso-8859-1' . "\r\n";