this is quite possible, but a really bad idea. perhaps you can share some more details about your initial requirements, end goals, and existing setup.
to be honest though, you don't need too much extra configuration to 'open up' access from any IP address. try first to configure SMTP authentication with the following directions and then see if it suits your needs:
http://tinyurl.com/2dfeef
let us know how you make out.
andrew