USPS Urges Customers to Switch from POSTNET to IMb Barcodes: This week saw USPS writing to 800,000 business mailers who hold a POSTNET permit to encouraging them to start making the transition to IMb. If they don’t make the switch by Jan. 28, 2013, those mailers will no longer be eligible for those mailers will no longer be eligible for discounts for business mail prepared to standards for automated processing.