] LOAF creates and maintains a database of all your
] correspondents, defined as people to whom you have sent
] email at least once. Every time you send an email
] message, LOAF appends this information to the email
] message, using a format described further below.
] LOAF-enabled correspondents collect and store this
] information in their own local databases.

Shared hashed white-lists. Interesting idea...

loaf