[Plugin: Contact Form 7] Send to based on field value

I’m looking to send to different email addresses based on a specific field value.

Field entered by user would be zip code(postal code) and the script then sends to a specific email address that responds to people in that zip code.

It should be fairly easy, I think, with some php and if statements, but I’m not sure where I would enter the code or if there is an easier way to accomplish this.