Their research resources may belong to the Internet age, but most charities still rely heavily on a distinctly low-tech fund-raising tool: direct mail. Indeed, nonprofits spent $1.8 billion on direct-mail solicitations last year. We asked experts to explain some of the strategy behind the carpet bombing. When Pasadena, Calif., marketing consultancy Russ Reid Co. asked donors how often they’d like to hear from their favorite charity, the typical answer was four times a year. But in follow-up tests, the firm found that fund-raising campaigns with 12 to 18 mailings a year were twice as profitable as those based on just three to six mailings. “It more than justifies the extra mailings and possible irritation factor,” says Russ Reid CEO Tom Harrison.