为什么这不起作用？

I've this little script to send email! But it's not working... Firstly it says that my variables are not defined and then, they confirm me that the message has been sent, but it doensn't happen!

Name:      
        <form action="contactus.php" method="POST">
            <input type="text" size="32" value="" name="name">
        </form> <br><br>
    E-Mail: &nbsp;&nbsp;&nbsp;&nbsp;
        <form action="contactus.php" method="POST">
            <input type="text" size="32" value="" name="header">
        </form> <br><br>
    Subject: &nbsp;&nbsp;
        <form action="contactus.php" method="POST">
            <input type="text" size="32" value="" name="subject">
        </form> <br><br>
    Message: <br>
    <form action="contactus.php" method="POST">
        <textarea rows="10" cols="40" name="message" value=""></textarea>
    </form>
    <br><br>

    <form action="contactus.php" method="POST">
        <input type="submit" value="Submit" name="submit">
    </form>


    <?php

    // php script to send emails 

    $to = 'some@email.com';

    if (isset ($_POST['message'])) {
        $message = "$name" . "<br><br>" . $_POST['message'];
    }


    if (isset ($_POST['header'])) {
        $header = "From:" . $_POST['header'];
    }


    if (isset ($_POST['subject'])) {
        $subject = ($_POST['subject']);
    }

    if (isset ($_POST['name'])) {
        $name = ($_POST['name']);
    } 




    if (isset($_POST['submit'])){
    mail($to, $subject, $message, $header);
    echo "Your message has been sent!";
    }



    //end of the php script

    ?>

If some of you can help me would be great!

Thank you.

You can't use all those different form elements. You are using 5 separate forms and the only one that is being submitted is the one with the submit button.

Thus, when the form is being submitted there $_POST['submit'] is set, but none of the other ones exist.

So you need your HTML to be:

<form action="contactus.php" method="POST">
    Name: &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
    <input type="text" size="32" value="" name="name"><br><br>
    E-Mail: &nbsp;&nbsp;&nbsp;&nbsp;
    <input type="text" size="32" value="" name="header"><br><br>
    Subject: &nbsp;&nbsp;
    <input type="text" size="32" value="" name="subject"><br><br>
    Message: <br>
    <textarea rows="10" cols="40" name="message" value=""></textarea><br><br>

    <input type="submit" value="Submit" name="submit">
</form>

and contactus.php:

<?php
$to = 'some@email.com';
if(isset($_POST['message']) && isset($_POST['header']) &&
   isset($_POST['subject']) && isset($_POST['submit']) &&
   @mail($to, $_POST['subject'], $_POST['message'], $_POST['header'])) {
    echo "Your message has been sent!";
}else{
    echo "There has been a problem.";
}
?>

Try:

if(mail($to, $subject, $message, $header)) {
    echo "Mail sent successfully.";
} else {
    echo "PHP's mail() function failed!";
}

Why you have a Form element for each input elements? You should put all of your elements in a Form together.