an extension to email that lets you send out address book data without compromising your privacy. LOAF appends a hash-like data structure to each outgoing email, and collects similar attachments from the people who write to you. These files can be queried to see if they contain a given email address, but they can’t be reverse-engineered to reveal the list of addresses used to construct them. LOAF lets you check whether someone emailing you for the first time is a complete stranger, or appears in the address books of some of your trusted correspondents. And as a decentralized application, LOAF offers an interesting alternative to current social networking sites like Orkut or Friendster.
The idea is to share your contacts with your friends via a hash of your addressbook. The hash uses Bloom filters. In fact, the social networking aspect is less networking than sharing who you trust as having sent you email that you’d like to read. You don’t have to network socially to do this really; it’s more about getting rid of spam. no central server so that’s nice. procmail can filter on incoming. but outgoing using pine, you fake sendmail to do the hash attachment.