Sovite

A modern, secure Mail Transfer Agent written in Elixir/OTP, meant as an alternative to Postfix.

Status: early development. Sovite receives mail over SMTP, queues it durably, and relays it to other servers with retries and bounces (Phases 1–2). It speaks TLS both ways (STARTTLS, implicit TLS, SNI, ACME, DANE) and accepts mail from authenticated clients on submission ports (Phase 3). It routes mail by its own database: hosted domains, aliases, mailboxes, transports, address rewriting, BCC, and access rules at every SMTP stage, all managed with sovitectl (Phase 4). It hands mail to mailbox servers such as Dovecot over LMTP, delivers to Maildir folders and pipe commands, detects mail loops, and can itself listen for LMTP (Phase 5). It checks SPF, DKIM, ARC, and DMARC on received mail, DKIM signs and ARC seals what it sends and forwards, rewrites forwarded senders with SRS, sends DMARC reports, and prints the DNS records a domain needs (Phase 6). It follows the DANE and MTA-STS policies of recipient domains, serves its own MTA-STS policy, sends TLS-RPT reports, and supports REQUIRETLS (Phase 7). It screens clients as postscreen does (greeting delay, weighted DNSBL, DNSWL, and RHSBL scores), greylists, checks reverse DNS and EHLO names, rate-limits clients and users, tarpits, refuses pipelining abuse, and suspends accounts whose mail bounces too much (Phase 8). It works with the Postfix ecosystem: milters such as Rspamd and OpenDKIM, policy servers such as postgrey and policyd-spf, after-queue content filters, HAProxy's PROXY protocol, XCLIENT and XFORWARD, and sendmail, mailq, and newaliases for local programs; sovitectl migrate postfix converts a Postfix configuration (Phase 9). It handles internationalized mail: SMTPUTF8 addresses, internationalized domain names (IDNA2008), UTF-8 header fields, and internationalized delivery status notifications, returning what a next hop without SMTPUTF8 cannot take (Phase 10). It speaks the additional ESMTP extensions: CHUNKING and BINARYMIME, DSN (with success notifications, RET, ENVID, and ORCPT), ETRN, MT-PRIORITY, FUTURERELEASE, DELIVERBY, and RRVS (Phase 11). It is run with sovitectl: the queue (list, show, flush, hold, release, delete, requeue), the configuration (show, diff, reload without downtime), how an address routes, status, message traces by queue ID or Message-ID, and pflogsumm-style log reports; it serves the web UI and an authenticated admin API (Plug and Cowboy), Prometheus metrics, and OpenTelemetry traces, logs to files, standard output, or syslog, drains gracefully on shutdown, integrates with systemd (notify, watchdog, socket activation, a hardened unit), and ships as a release tarball, .deb and .rpm packages, and a container image (Phase 12). Several servers can run as one cluster over Partisan, with mutual TLS between the nodes: they share a configuration pushed to all of them, rate limits, bans, and greylisting, keep copies of each other's queues and deliver the mail of a node that stays down, hand a leaving node's queue to the others, and can send all mail for a destination from one node; it hosts tenants with their own limits, DKIM keys, and IP pools, and sends from outbound IP pools with warm-up schedules and daily limits (Phase 13). Hardening for 1.0 is next. See the roadmap.

Sovite is also a library: its components (address validators, DNS and MX resolution, an SMTP server and client, TLS with DANE and ACME, SASL, LDAP, RFC 5322 address lists, delivery status notifications, and later DKIM, SPF, ...) can be used from any Elixir project without running the MTA. See STRUCTURE.md.

Development

Requires Erlang/OTP 29 and Elixir 1.20 (see mise.toml).

mix setup           # deps.get
mix test            # tests, including property tests
mix lint            # format check, warnings as errors, credo, xref cycles
mix dialyzer

The first Dialyzer run builds its PLT and takes a few minutes; later runs are incremental.

Manage routing data (stored in Sovite's database):

sovitectl domain add example.com hosted
sovitectl mailbox add alice@example.com
sovitectl alias add sales@example.com alice@example.com bob@example.com
sovitectl transport set example.com lmtp:unix:/run/dovecot/lmtp
sovitectl access set client 192.0.2 REJECT spam source   # used by client_access in [restrictions]

Run the MTA locally:

mix dev.mta         # the MTA: SMTP on 127.0.0.1:2525, web UI and admin API on 127.0.0.1:9025
mix dev             # the MTA and the web UI's dev server (bun dev, http://localhost:5173)
iex -S mix dev.mta  # with a shell

They use --config PATH, $SOVITE_CONFIG, or sovite.toml in the project if one of them is given; otherwise they write development/sovite.toml, with data in development/, local mail for sovite.test in Maildir folders there, and other mail relayed to 127.0.0.1:1025 for a mail catcher such as Mailpit, never to the internet. They print the admin token to sign in to the web UI with. The web UI's own checks run in the project root: bun run check, bun run lint, bun run test.

Build a release:

MIX_ENV=prod mix release
_build/prod/rel/sovite/bin/sovitectl config check _build/prod/rel/sovite/etc/sovite.toml.example
SOVITE_CONFIG=/etc/sovite/sovite.toml _build/prod/rel/sovite/bin/sovite start

Documentation

License

AGPL-3.0. See LICENSE.