Fix my PHP script to parse forwarded emails

I have a script (attached) that parses emails read in from STDIN. It works great for original emails, but now I need it to work if the email is forwarded. The result I want is to have [login to view URL] updated so $body will store the value of the original email's body. The script will need to work for emails forwarded from all major email hosts. This example email ([login to view URL]) is an email forwarded from gmail, but I want the script to be universal. I have included [login to view URL] just to show how a regular email works with the script.