Each layer in Alice's inbox only displays emails from;
Layer 2.1 (tofu): an address not in contact book, sharing with an address block of people they want to be interested
Examples: unsolicited notifications and marketing "newsletters" from domains you have an account with. Begmail from charities and political parties.
Layer 2.2 (spam): an automated mailer, to any address block of people they can find
(3/?)