Fix: web-form autoresponder issues

[shall]

We migrated a site from Plesk 8 for Linux to Plesk 8 for Windows, but the autoresponders that were previously set up started responding ONLY to the PHP sender/anonymous account.

We fixed this by adding a "Return-Path" header to the message in the 4th mail() parameter ($email is the users email address):
mail($to, $subject, $msg, "Return-Path: <$email>\r\n");