Firms who regularly have large quantities of commercial printed papers such as catalogues, prospectuses, price lists etc. which are excluded from the bulk rate per bag may apply to the Postmaster General for a permit to imprint a Postage Paid design on the envelopes of wrappers. The addressed items may then be handed in at a designated post office without further need for postage stamps or other indication of payment.
A permit account number is starting with prefix PM or PT (for iMail).