Return-Path: problems

I've written a script which is suppose to send e-mail using the mail() function. This it does alright, but if the mail address is invalid then it return via the Return-Path: header address which is set by the webserver. I've tried passing it in as an extra param to te mail() function but I don't seem to be able to set it. How can I go about doing this as the admin of the server is getting irate at constantly getting e-mail about telling him an e-mail was undeliverable. And I don't want asking him to change the web server settings as this would affect any other users in the future who wish to use the mail function. Cheers. Dave. -- They are amongst us!