Free and green. Those are the goals of a pilot program launched recently by the U.S. Postal Service that allows customers to recycle small electronics and inkjet cartridges by mailing them free of charge. The âMail Backâ program helps consumers make more environmentally friendly choices, making it easier for customers to discard used or obsolete small electronics in an environmentally responsible way. Customers use free envelopes found in 1,500 Post Offices to mail back inkjet cartridges,