Parsing received email

I've got an email address set up so that is an alias for a PHP script. IE, if you send an email to that particular address, the email is passed off to the script and it reads it in and processes it. All of this is working find and well. I can do a regex on every line to determine who the email was to, from, subject, etc. However, what I am having problems with is that the rest of the email header isn't the same depending on what email client is used to send the email in the first place. So with that in mind, is there any way to tell when the headers stop and the actual body begins? Chris