PHP mail() headers

[okendoze]

I stumbled across a mail script so long ago, I can't remember where. The person who wrote it included a bunch of headers, I might guess every type of header you can possibly use with PHP (but I don't know much about it).

I'd like to know what headers are necessary and which are recommended, whether or not they're they're in this script I have.

I'd also like to know if the ini_set line is necessary.

& if you have any other advice concerning PHP mail, kindly fill me in. Thanks.

$sender_name="";
$sender_to=$_POST["email"];
$sender_from=$_POST["sender"];
$subject=$_POST["subj"];
$message=$_POST["msg"];

$to=$sender_to;
$from=$sender_from;

ini_set(sendmail_path, "/usr/sbin/sendmail -t -f $from");

$date= date("r");

$headers = "From: $sender_name<$from>\n";
$headers .= "Reply-To: $sender_name<$from>\n";
$headers .= "X-Sender: $sender_name<$from>\n";
$headers .= "X-Mailer: PHP4\n";
$headers .= "X-Priority: 3\n";
$headers .= "Content-Transfer-encoding: 8bit\n";
$headers .= "MIME-Version: 1.0\n";
$headers .= "X-MSMail-Priority: High\n";
$headers .= "Importance: 3\n";
$headers .= "Date: $date\n";
$headers .= "Delivered-to: $to\n";
$headers .= "Return-Path: $sender_name<$from>\n";
$headers .= "Content-Type: text/plain; charset=UTF-8\n";

mail($to,$subject,$message,$headers); 

[whirlwind]

As far as I am aware you only NEED the following. I assume that not including a 'from' address will get you recognised as spam. Anything else is extra. I only use the following for simple scripts.

$to=$_POST["email"];
$from=$_POST["senders_email"];
$subject=$_POST["subj"];
$message=$_POST["msg"];

$headers = "From: $from";

mail($to,$subject,$message,$headers);