  We describe a simple approach to peer-to-peer electronic mail that would
allow users of ordinary workstations and mobile devices to exchange messages
without relying upon third-party mail server operators. Crucially, the system
allows participants to establish and use multiple unlinked identities for
communication with each other. The architecture leverages ordinary SMTP for
message delivery and Tor for peer-to-peer communication. The design offers a
robust, unintrusive method to use self-certifying Tor onion service names to
bootstrap a web of trust based on public keys for end-to-end authentication and
encryption, which in turn can be used to facilitate message delivery when the
sender and recipient are not online simultaneously. We show how the system can
interoperate with existing email systems and paradigms, allowing users to hold
messages that others can retrieve via IMAP or to operate as a relay between
system participants and external email users. Finally, we show how it is
possible to use a broadcast protocol to implement mailing lists and how
distributed ledger technology might be used to bootstrap consensus about shared
knowledge among list members.
