what would return?

Hi, I have a php script that will send certain information to a mailing list. Upon arrival the customer will have seven records each with a unique id. On clicking the link a mail will be sent back with the subject having that unique id. On arriving at my mail server I pipe the mail thru a php program using lynx -dump http://localhost/filename.php > /dev/null. My question is what will be returned to the filename.php. I need the unique id from the subject to do further processing? Any ideas. Adrian