(poss OT) mail() function

hi all We have a web based employment site, running on PHP and MySQL (to all those didn't know!). Whenever a candidate sees a job they're interested in they click a button and an email is sent to our consultants for them to act on. The problem, little as it is, is that I've written a function to send the email (copied below) and sometimes (more often than not) the email is fine (I get a copy), but other times it's all plain text and the formatting isn't there. Does anyone know why this would happen? Cheers in advance Dave // start copy of function function send_email($whoto,$whofrom,$subject,$message) { $subject = "[AUTOMATED NOTIFICATION] - $subject"; $mailheaders = "Content-Type: text/html; charset=iso-8859-1"; // Mime type mail($whoto, $subject, $message, $mailheaders); } // end copy of function