Baltimore--Advertising.com, pushing to establish itself as a major e-mail direct marketing agency, announced Tuesday it has acquired OakNet Publishing for an undisclosed sum. Advertising.com said the acquisition pushes its direct messaging audience to more than 5 million addresses. OakNet, Gainesville, Fla., distributes and sells advertising for 90 Internet newsletters and claims more than 175,000 readers. Included on its newsletter list are titles serving marketing and advertising executives, Internet start-ups and the accounting industry. After the acquisition is complete, Advertising.com will reach 700 specialized newsletters.