Email Verication Code Setup

In need of a programmer to write a script on my site which can do these things. 1) Allow the admin to manage the sending of messages 2) Block IP addresses from accessing the site and sending messages 3) Block email addresses from sending messages 4) Block email domains from sending messages 5) Setup (gd2) verification code for all communications - (allow admin to enable/disable this feature) 6) Setup moderation of all messages - when a message is sent to a user, it will not arrive to the users inbox until the admin has released the message (allow admin to enable/disable this feature) **I am attempting to get control of the SPAM which is being unleashed on my site. The site is a local online classified ad service which anyone with internet connectivity can contact the seller through a contact form. Recently users of my site have been getting SPAM emails because it seems SPAMMERS may be running scripts against my site. Currently I have no SPAM control implementation and that is what I need from you. If you have any other ideas of how to defeat SPAM on my site then please feel free to enlighten me. System Details: Dedicated server: Windows 2003 Server, IIS 6.0, MySQL 4.1, PHP5 Access: FTP, PHPMyAdmin