Bcc is set by adding something like this to the additional headers parameter:

"Bcc: copyme@example.com\r\n"

This should work from PHP 4.3 onwards.

If you don't feel like writing the headers yourself, you might find it easy to use the PHPMailer class. It's quite professional and allows cc, bcc, multiple addresses, smtp authentication, attachments and so on.

You will need to download the classes from http://phpmailer.sourceforge.net/ and then use some code like this :

require("class.phpmailer.php");

$mail = new PHPMailer();

$mail->IsSMTP(); // send via SMTP
$mail->Host = "smtp1.site.com;smtp2.site.com"; // SMTP servers
$mail->SMTPAuth = true; // turn on SMTP authentication
$mail->Username = "jswan"; // SMTP username
$mail->Password = "secret"; // SMTP password

$mail->From = "from@email.com";
$mail->FromName = "Mailer";
$mail->AddAddress("josh@site.com","Josh Adams");
$mail->addBCC("joe@site.com","Joe Tailer");

$mail->Subject = "Here is the subject";
$mail->Body = "This is the body";


if(!$mail->Send())
{
echo "Message was not sent <p>";
echo "Mailer Error: " . $mail->ErrorInfo;
exit;
}

echo "Message has been sent";

thanks a lot, that's a great help.
Especially the phpmailer class makes things easier for me. Thanks for the example, redcharcoal.

AddBCC will work only on Win32 :(