Square, the mobile payment startup, introduced Square Cash, which is their form of sending and receiving cash over email. The service, much like Google Wallet, Venmo, and others, lets you send money by simply adding the amount of money you wish to send as the subject line and copying [email protected] on the message. To receive the money, you just click through the email onto the Square Cash website, where you enter the debit card information for the account you want to transfer the money into. It works with any email address, and provided you have square, you’re all set. It’s another very viable player in the mobile payments sphere that’s increasingly heating up.