MailBlocks is an e-mail hosting service company based in the United States, originally established by Phil Goldman in 2002.
[2] Mailblocks did not invent challenge response to block spam.
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.
For example, David Skoll described it in detail in a post to a public forum on November 15, 1996.