PHP Contact Form Blank Data & Unknown Sender - php

Question

Hello I have made a contact form on my website but even if the user doesn't type in any of the details and presses the submit button it sends me a blank email with nothing in it from Unknown Sender.
Anyone know why this is happening? I have added form validation so it shouldn't be sending anything.
HTML Code:
<form action="mail.php" method="POST">
<font color="red">*</font> Name <input type="text" name="name" required>
<font color="red">*</font> Phone <input type="text" name="phone" required>
<font color="red">*</font> Email <input type="text" name="email" required>
<font color="red">*</font> Message <input type="text" name="message" placeholder="I am looking for..." required><br />
<input type="image" src="images/Landing_Pages/submit.png" border="0" alt="Submit" />
</form>
PHP Code:
<?php $name = $_POST['name'];
$phone = $_POST['phone'];
$preferred = $_POST['preferred'];
$email = $_POST['email'];
$formcontent="From: $name \n Phone: $phone \n Email: $email \n Message: $message \n Preferred Contact: $preferred \n Email: $email";
$recipient = "bwebb#webbmaster.com.au";
$subject = "New Request Southbank";
$mailheader = "From: $email \r\n";
mail($recipient, $subject, $formcontent, $mailheader) or die("Error!");
?>

Answer 1

You have to check if post data is not empty
if (!empty($name) && !empty($phone) && !empty($preferred) && !empty($email)) {
mail($recipient, $subject, $formcontent, $mailheader) or die("Error!");
}
Edit
<?php
$name = $_POST['name'];
$phone = $_POST['phone'];
$message = $_POST['message'];
$preferred = $_POST['preferred'];
$email = $_POST['email'];
$formcontent="From: $name \n Phone: $phone \n Email: $email \n Message: $message \n Preferred Contact: $preferred \n Email: $email";
$recipient = "bwebb#webbmaster.com.au";
$subject = "New Request Southbank";
$mailheader = "From: $email \r\n";
if (!empty($name) && !empty($phone) && !empty($message) && !empty($preferred) && !empty($email)) {
mail($recipient, $subject, $formcontent, $mailheader) or die("Error!");
}
?>

Answer 2

Do something like :
$errorflag = 0 ;
if(empty($name)){$errorflag = 1 ;$error = "Input your Name plz!"; };
if(empty($phone)){$errorflag = 1 ;$error = "Input phone"; }
...
if(!$errorflag) {
#mail($recipient, $subject, $formcontent, $mailheader) or die("Error!");
}
check every input you need and then send