NSM FormMail Script

I'm using the NMS FormMail, and I wanted to configure it so that it can be used on any host or server without chaning anything. One of the main things is that I want referrers to not have to be changed, but I also don't want it to work except on the host it's uploaded to. I tried just putting localhost in the referrers field, but I still get the error that the domain needs to be in the referrers field.

How can I make it work anywhere, assuming it's on that server?