The "$to" variable is who it is sending it to. Of course you wont recieve the email if the "$to" variable changes.
Also, if you are submitting the form Via POST then you cannot use the GET function, you have to use POST. All forms should be submitted via POST anyway.
This is how it should be done...
<?
$to ="youremailaddress@whereever.com; //where the email is being sent.
$namenew = $_POST['name']; //Users Name
$emailnew = $_POST['email']; //Users Email
$subjectnew = $_POST['subject']; //Subject of the email
$feedbacknew = $_POST['feedback']; //Comments of the email
$subject = "Model Contact Us $emailnew";
$matter = "Below are the details filled by $namenew\n\n
Name: $namenew\n\n
Email: $emailnew\n\n
Subject: $subjectnew\n\n
Comments: $feedbacknew\n\n";
mail($to, $subject, $matter, "From: $emailnew");
?>