Definition of white mail

correspondence received from customers in their own envelope rather than in an envelope provided by the marketer. White mail generally contains address-change requests, complaints, inquiries, and orders. Customers sometimes want to send payment along with a business reply card or space ad order and will therefore enclose the card in an envelope along with their check. White mail typically takes two to three times longer to process than reply envelope mail, because the variety of envelope sizes makes machine opening slow and the variety of items enclosed must be sorted according to the type of processing required.