Business reply mail

Freepost is a postal service provided by various postal administrations, whereby a person sends mail without affixing postage, and the recipient pays the postage when collecting the mail. Freepost differs from self-addressed stamped envelopes, courtesy reply mail, and metered reply mail in that the recipient of the freepost pays only for those items that are actually received, rather than for all that are distributed.

In one typical use of freepost, a business sends bulk mail to potential customers, the bulk mail including envelopes or postcards that potential customers can return to the business by freepost. In another typical use, magazines include subscription cards that potential subscribers can return by freepost. In yet another typical use, a seller can provide a merchandise return label bearing the appropriate freepost indicia (as described below) to a customer so that the customer can return the item to the seller by freepost upon issuance of a Return Merchandise Authorization.

A non-commercial usecase would be to return lost items belonging to some business: the item will have printed on the back "if found please return by freepost to <address>". For example, UK's NHS worker's RFID access cards can be returned by freepost if lost & found.

In Australia, freepost is called Reply Paid. Specially printed envelopes are used, with the permit holder's address, the words "Reply Paid" with an authorization number. The stamp is replaced by three black stripes. The permit holder pays the postage plus a fee to the postal authority. The customer may write the Reply Paid envelope out by hand.

An important customer like the Taxation Office would have an RP number the same as the post code, to minimize errors even more.

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Wikipedia