..
  This file is part of PEPSI.
  Copyright (C) 2026 Pepsi contributors

  PEPSI is free software; you can redistribute it and/or modify it under the
  terms of the GNU Affero General Public License as published by the Free
  Software Foundation; either version 3, or (at your option) any later version.

  PEPSI is distributed in the hope that it will be useful, but WITHOUT ANY
  WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
  A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
  details.

============
Pepsi Manual
============

Pepsi is an e-mail **forwarding pipeline and crypto gateway** written in Rust. It
receives mail over SMTP, authenticates it at the boundary, and then advances each
message through a configurable chain of small *stage programs* — ARC sealing, SRS
envelope rewriting, end-to-end encryption and decryption, DKIM signing, bounce
generation and delivery (direct-to-MX, via a smarthost, or locally) — that
together re-send the mail while preserving the authentication verdicts the final
receiver needs.

Unlike a classical store-and-forward MTA, Pepsi is structured as a series of
independent programs chained over a **single shared database table**. Each
processing step is its own program, so the pipeline can be reordered, individual
steps replaced, and new behaviour added by dropping in another program — without
touching the rest of the system.

Start with :doc:`introduction`, which says what Pepsi is, lists its key
features, compares it with the established MTAs and explains how the rest of
this manual is organised. :doc:`getting-started` is the walkthrough from DNS
to a first received e-mail, and :doc:`wizard` shows the pipelines
``pepsi-setup --wizard`` builds and what each of its questions decides.

.. toctree::
   :maxdepth: 2
   :numbered:
   :caption: Contents

   introduction
   getting-started
   installation
   packages
   wizard
   configuration
   features
   smtp-extensions
   key-management
   secure-link
   interoperability
   security
   exchange
   admin-api
   web-ui
   architecture
   state
   extending
   testing
   benchmarks
   performance
   programs/pepsi-ingress
   programs/pepsi-dispatch
   programs/pepsi-httpd
   programs/pepsi-stage-arc
   programs/pepsi-stage-srs
   programs/pepsi-stage-encrypt
   programs/pepsi-stage-decrypt
   programs/pepsi-stage-dkim-sign
   programs/pepsi-stage-bounce
   programs/pepsi-stage-aliases
   programs/pepsi-stage-relay-to-internet
   programs/pepsi-stage-relay-to-smarthost
   programs/pepsi-stage-relay-to-maildir
   programs/pepsi-stage-dot-forward
   programs/pepsi-stage-relay-to-lmtp
   programs/pepsi-stage-discard
   programs/pepsi-stage-anti-spam
   programs/pepsi-stage-auto-pay
   programs/pepsi-stage-check-whitelist
   programs/pepsi-stage-auto-whitelist
   programs/pepsi-stage-autocrypt-learn
   programs/pepsi-stage-detect-language
   programs/pepsi-detect-language
   programs/pepsi-stage-block-language
   programs/pepsi-stage-vacation
   programs/pepsi-stage-edit-settings
   programs/pepsi-stage-if
   programs/pepsi-stage-milter
   programs/pepsi-stage-route
   programs/pepsi-stage-vks-confirm
   programs/pepsi-stage-secure-link
   programs/pepsi-setup
   programs/pepsi-queue
   programs/pepsi-status
   programs/pepsi-sendmail
   programs/pepsi-whitelist
   programs/pepsi-keys
   programs/pepsi-keydisc
   programs/pepsi-settings
   programs/pepsi-tlsrpt
   programs/pepsi-secure-link
   programs/pepsi-failure-bouncer
   programs/pepsi-quota
   programs/pepsi-helper-token-refresh
   programs/pepsi-telemetry
   programs/pepsi-telemetry-client
   programs/pepsi-config
   feature-stability
   manpages/index
   rfc-index

Indices
=======

* :ref:`genindex`
* :ref:`search`