The initiative is aimed at increasing the use of environmentally friendly materials in bulk mailings in return for discounts of up to 4.7% on standard Mailsort prices.
Both companies anticipate starting mailings through the scheme next month, while Royal Mail claims more than a dozen other businesses will also soon be on board.
In order to qualify for the discount, companies need to meet three criteria, which are improved sustainability, minimised waste and increased recyclability.
The cost reduction available for Sustainable Mail with Mailsort 120 or 700 is 2% for entry level or 4.7% for intermediate level.
At entry level for Mailsort 1400, the reductions range from 2% to 1.05%, depending on item format and whether there is direct or residue selection, and for intermediate level they range from 4.7% to 2.55%.
Paul Twiggs, head of marketing and sales development at Black Horse Personal Finance, said: "Direct mail is an integral part of our marketing strategy and Sustainable Mail helped us to improve on the strides we had already taken to make our campaigns even more environmentally friendly."
Elsewhere, TNT Post has teamed up with the Direct Marketing Association (DMA) to promote environmental best practice within the direct mail arena.
Both parties have signed a letter that calls for joint on-going initiatives that commit to the responsible use of direct mail.
Gillian Lyall, who chairs the DMA's mailing houses council, said the signing "indicates the DMA and TNT Post's commitment to both the continued growth of the sector and the environment".
See also:
Antalis leaflet outlines new Royal Mail cost reduction scheme
