The association has more than 919 business members who pay an annual fee to use its services, but only 27 charities currently subscribe.
"Charities are major users of direct marketing, but they aren't joining, so we need to get closer to them and find out what their needs are," said Mike Barnes, director of marketing and business development at the DMA. "We want to engage charities and get them networking in a direct marketing arena."
Barnes said the DMA plans to invite about 250 charities to the event, which is to be held later this year, and hopes for backing from the Institute of Fundraising.
He added: "We need to make sure people know what the DMA has to offer and recognise its value."