AOL described the acquisition as its latest effort to battle spam, or unsolicited email, which continues to plague consumers and businesses alike.
Privately held Mailblocks sells anti-spam software based on "challenge-response" technology that requires senders not on a person's approved list to reply to a question before their message will be received. The system is designed to thwart spam generated by machines, which cannot reply to the question.
AOL said it plans to add Mailblocks' software to its existing anti-spam tools through a series of upgrades. The company also intends to completely redesign the Web-based email systems offered on both its AOL and its Netscape sites, adopting Mailblocks' user interface in an effort to make the sites faster and simpler to use.
An AOL representative said the company has been a "long-time admirer" of Mailblocks technology and views the buyout as a favourable addition to its collection of anti-spam technology.
"This acquisition speaks volumes about AOL's commitment to providing the best email and spam-fighting tools to our members, as well as our overall, ongoing commitment to the battle against unwanted junk email and the spammers who try to send it," Roy Ben-Yoseph, director of email products at AOL, said in a statement.
Earlier this year, the ISP reported that it had blocked more than 1 billion virus-infected emails since launching a screening program in April 2003. AOL claimed that it protected each of its subscribers from an average of 30 virus attacks during that period.
Company executives were quick to point out that AOL's acquisition of Mailblocks does not indicate a departure from the ISP's work on an industrywide authentication protocol standard for preventing email forgeries. That standard was formerly known as Sender Permitted From and recently renamed Sender Policy Framework, or SPF. Rather, they said, the two systems would complement each other after they have been further developed.
Because AOL is the world's largest ISP, its endorsement of SPF is seen as critical to the evolution of a long-sought email verification standard and could encourage other major email providers to implement the guideline.
Mailblocks lost its founder and chief executive, Phil Goldman, when the executive died unexpectedly at the age of 39 last December. Goldman was best known as one of the founders of WebTV and had also worked previously at Apple.
