Unsolicited bulk electronic mail (spam) is increasingly plaguing the Internet Email system and deteriorating its value as a convenient communication tools. In this paper we argue that the difficulties in controlling spam can be attributed to the lack of receiver control on how different Email messages should be delievered on the Internet. In the current Email delivery architecture, a user can send messages to another at will, regardless of whether or not the latter is willing to accept the message. Based on this observation, we propose a differentiated message delivery architecture—DiffMail. In DiffMail, a user can classify Email senders into multiple classes and handle messages from each class differently. For example, although a receiver may directly accept messages from the regular correspondents, he may selectively ask other senders to store messages on the senders’ own mail servers, and pull the messages only if and when he wants to. In this paper we present the DiffMail arc...