299506 Modify simple php mail script

I have a mailer script that allows me to send email from a form which automatically creates the reply to address from server environment. Problem is, if the server domain starts with [login to view URL] vice [login to view URL], the reply address has this incorrect domain in it as well. I need the script to parse the www out of the domain only when it is presnt ( iuse this script on a number of sites)