Although it isn't meant for merchant transactions, Square Cash, the service that lets you transfer money by email, can come in handy in business situations.

Now Square Cash--an offshoot of Square Inc., the mobile payments startup (and recent Inc. audacious company) helmed by Twitter co-founder Jack Dorsey--has rolled out a nifty free feature allowing users to request payments from one or more people via email.

All you have to do is enter "request@square.com" into the "cc" field in an e-mail client or the Square Cash app, and then send the message to your contacts. There's one minor caveat: Only one monetary amount can be entered into the subject field. You can't ask for different amounts from people in a single email.

To make and receive payments, the parties on both ends of the transaction connect their email account to a debit card.