$to  = 'exemple@example.com';
$subject = 'sujet';
$headers = "MIME-Version: 1.0\r\n";
$headers .= "Content-type: text/plain; charset=utf-8\r\n";
$message = 'ligne 1\n';
$message .= 'ligne 2\nLigne 3\n';
$message .= 'ligne 4\n';
...
mail($to, $subject, $message, $headers);