"Can't take it with you? Mail it instead," reads a sign posted on one of ReturnKey Systems' Automated Mailing Kiosks (AMKs) in the Newark Liberty International Airport. Thanks to ReturnKey and the company's AMK system, airline travelers no longer must forfeit personal items to the Transportation Security Administration, which since 9/11 has been commissioned to keep airlines free of any potential weapons. With the kiosks, items that would've been confiscated can now be mailed ahead. The AMKs look much like ATMs. There's a touch screen where users can enter information and access directions, along with a mail slot for sending...