Building a Bulletproof Contact Form with PHP
http://www.digital-web.com/articles/bulletproof_contact_form_with_php/

Pennell, Matthew
Digital Web Magazine
2007

Abstract:

The humble contact form: It's the cornerstone of nearly every website, from the humble personal blog right up to the corporate megasite--and a billion small business sites in-between. In the early years of operating a website, we were happy to put our shiny new email address out there for anyone to mailto, but the rise of the spammer has made us justifiably wary of publicizing our contact details--enter the contact form.