Do not mix the message body with the extra headers mail has five parameters which are To, Subject, Message, Additional Headers, Additional parameters
so your mail would look something like
mail("someone@ahost.com", "Php e-mail", $message,$heasers);
your headers which contain such things a text type From: Reply-to: and so on go in the $headers (additional headers) so the headers would look something like
$headers = 'MIME-Version: 1.0' . "\r\n";
$headers .= 'Content-type: text/html; charset=iso-8859-1' . "\r\n";
$headers .= 'From: youremail@somehost.com' . "\r\n" .
'Reply-To: youremail@somehost.com' . "\r\n" .
'X-Mailer: PHP/' . phpversion();
Also keep in mind that lines of text should not exceed 72 characters so you might want to use the wordwrap() function like
$message = wordwrap($messagebody,72,"\n<br>");