MailBlocks

MailBlocks is an e-mail hosting service company based in the United States. It was acquired by AOL on August 3, 2004. Phil Goldman set up the firm.
Service.
Mailblocks offered free challenge-response spam filtering web email service and an IMAP interface as a revenue service.
Patent Troll Controversy.
Mailblocks did not invent challenge response to block spam. Instead, they purchased the rights to two patents related to challenge response: patents US6199102 and US6112227. Mailblocks then proceeded to patent troll several other companies before releasing any product of their own. Companies sued included Spam Arrest, DigiPortal, MailFrontier, and Earthlink. It is worth noting that challenge response was a well known technique for fighting personal spam and mailing list spam for years before the two patents were applied for. For example, David Skoll described it in detail in a post to a public forum on November 15, 1996. Some say MailBlocks was an early example of a patent troll. Patent trolls are possible because they ask for licensing fees that are far less than what it would cost for the companies to defend themselves successfully in court. Patent trolls are less of a problem in Europe than in the United States due to a loser pays cost regime.