"From field" in PHP email form

[sammymaudlin]

I used a wizard to create a PHP email form.  I was able to customize it with the exception of the From field.  I need the email that is sent to be "From" the email that the sender input.  Instead it comes "From" a nonexistent email address with "server" in the domain.  Here is the processor code I'm using

<?php

$where_form_is="http://".$_SERVER['SERVER_NAME'].strrev(strstr(strrev($_SERVER['PHP_SELF']),"/"));


mail("braintrack@yahoo.com", $_POST['field_3'], "

First Name: " . $_POST['field_1'] . "
Last Name: " . $_POST['field_5'] . "
Email Address: " . $_POST['field_2'] . "
Situation: " . $_POST['field_3'] . "
Message: " . $_POST['field_4'] . "




");

include("confirm.html");

?>

Any help would be greatly apprciated.