HTML联系表单不起作用

I have a contact form on my webpage so I sen me messages by email but it doesn't work.

I tried to send a message by using the PHP code on GET mode and manual parameters

<a href="contactpage.php?name=name&email=em&message=men">send</a>

and it works, so maybe the error is on HTML code.

HTML code:

<form id="contactForm" class="contact-form" name="formulario" method="post" action="contactpage.php">
    <div class="form-group form-icon-group">
        <input class="form-control" name="name" placeholder="Nombre" type="text" required/>
        <i class="fa fa-user"></i>
    </div>
    <div class="form-group form-icon-group">
        <input class="form-control" name="mail" placeholder="Email" type="text" required/>
        <i class="fa fa-envelope"></i>
    </div>
    <div class="form-group form-icon-group">
        <textarea class="form-control" name="mes" placeholder="Mensaje" rows="10" required></textarea>
        <i class="fa fa-pencil"></i>
    </div>
    <div class="text-center">
    <input type="submit" name="submit" value="Envía tu solicitud" class="btn btn-primary">
    </div>
</form>

and the PHP code:

<?php
$nombre = $_POST['name'];
$email = $_POST['mail'];
$mensaje = $_POST['mes'];

$header = 'From:'. $email."
";
$header.="X-Mailer: PHP/". phpversion(). "
";
$header .= "Mime-Version: 1.0 
";
$header .= "Content-Type: text/plain";

$mensaje = "Este mensaje fue enviado por " . $nombre . ", con email " . $email . " 
"; 
$mensaje .= "Su e-mail es: " . $email . " 
";
$mensaje .= "Mensaje: " . $_POST['mes'] . " 
";
$mensaje .= "Enviado el " . date('d/m/Y', time());

$para = 'myemail@email.com';
$asunto = 'Contacto desde la web';

$bool = mail($para, $asunto, utf8_decode($mensaje), $header);

if($bool){
    echo "Mensaje enviado";
}else{
    echo "Mensaje no enviado";
}
?>

Thank you all!

$to      = 'email@example.com';
$subject = 'the subject';
$message = 'hello';
$headers = 'From: webmaster@example.com' . "
" .
    'Reply-To: webmaster@example.com' . "
" .
    'X-Mailer: PHP/' . phpversion();

mail($to, $subject, $message, $headers);

http://www.php.net/manual/en/function.mail.php