PHP Warning: mail() has been disabled for security reasons in

Estou com um problema num formulário de enviar email.

Ele mostra a mensagem a dizer que envia mas depois não recebo o email.

E gera um erro :

[04-Jul-2016 11:26:47 Europe/Lisbon] PHP Warning: mail() has been disabled for security reasons in /home/psicosso/public_html/teste/processEmail.php on line 32
[04-Jul-2016 11:51:03 Europe/Lisbon] PHP Warning: mail() has been disabled for security reasons in /home/psicosso/public_html/teste/processEmail.php on line 18

O código é o seguinte:

<?php

//create short variable names

//modify the next line with your own email address
$to = 'estudio@desigm.pt'; // Replace with your email

$subject = $_POST['subject'];
$message = $_POST['message'] . "\n\n" . 'Cumprimentos, ' . $_POST['name'] . '.';
$headers = 'From: ' . $_POST['name'] . "\r\n" . 'Reply-To: ' . $_POST['email'] . "\r\n" . 'X-Mailer: PHP/' . phpversion();

switch ($valid) {

case 0:

 mail($to, $subject, $message, $headers);
 //clear the variables
 $name='';
 $email='';
 $subject='';
 $message='';
 echo 'response=passed';
 break;
 case 1:
 echo 'response=invalid';
 break;
 case 2:
 echo 'response=error';
 break;

}//end switch

?>

Alguem me pode ajudar??