The script called "formmail" is CGI, not PHP and can be found at [scriptarchive.com...] However there are lots of PHP equivalents. If you can't find one on www.hotscripts.com, also try www. scripts.com and [php.resourceindex.com...] If you need any more help, please ask.
The original "formmail" from Matt's Script Archive is plagued with security holes - even Matt himself does not recommend using it. Rather he suggests the rewrite called NMS-Formmail. You can download it here: