The company's Mailsort service uses a barcode and a computer-readable typeface on mailings. It is cheaper to process because it eliminates hand sorting. Charities that use the service are charged up to 2p less per item.
The RNLI saved £18,615 last year by moving supporter mailings to machine-able mail, and the National Trust saved £20,000 in postage.
The trust was initially worried that sending out mail with barcodes would have a negative effect on creativity and response rates.
However, after the switch, response rates rose from 1.13 to 1.16 per cent. In addition to the savings, this led to a £15,000 increase in income for the charity.