Since it began collecting statistics in 2004, the volume of mailings has grown steadily from 340m in 2004 to 412m in 2007 but the number of mailings dropped by 0.7% to 409m in 2008.
The increasing popularity of digital communications for charities is one likely factor behind the fall but but one observer attributed these figures to a decrease in volume from big cold recruiters, who were failing due to a lack of targeting. He advises charities to spend more on retaining existing donors.
Royal Mail said that there had been a decline in overall direct mailing since a peak in 2005.
Last week the Royal Society for the Protection of Birds said that it was switching from direct mail campaigns to online fundraising appeals following requests from supporters for e-communications.
The charity said that it had previously sent out appeals as direct mail but is now keen to develop its digital communications strategy and explore more cost-effective fundraising ideas.
More than half of charities (52%) admitted that they were feeling the effects of the recession in February, according to the Charities Commission's latest survey, compared with 38% when the survey was carried out in September.
About a third of charities admitted they were suffering a decline in income as a result of the financial crisis.