by parameters, i assume you mean headers - like from, to, cc, bcc etc etc
custom headers normally begin with x-, ie if you wanted to add a header for users ip, you would add it as x-ip
then, you just add it to the headers (with \r\n between)
mail( "me@domain.com", "Feedback", "$message", "From: $email\r\nX-ip: 192.168.0.1" );
like that!
adam