PHP intercepting incoming email

I am not at all sure what is involved with something like this so I am not even sure where to start looking. I'm hoping someone would be able to point me in the right direction and not necessarily tell me how to do it (unless you really wanted to :p). I want to be able to send an email to a particular email address. Once it's received on our server, the server would see that to that special address and transfer controle to PHP which would then process that email. Where would I go to learn how this can be done? Chris