mixandClaude Opus 5.5
d398f488e2
Closes what the security review left as an accepted risk: with the
spam filter down - it is attached fail-open - nothing removes verdict
headers a sender wrote himself, and the inbound journal recorded his
verdict as the filter's. The owner asked whether rspamd could add a
header that proves the others are ours (2026-10-12) and agreed to a
signature: a fixed mark could be written by a sender as easily as the
verdict.
- inbound.FilterKey: a key of 32 random bytes, 64 hex characters, in
/data/antispam/filter.key, made on the first start with the relay
on. 0644 like the list files beside it: the filter is another user
in another container.
- deploy/antispam/rspamd/milter_headers.conf: a custom routine reads
the key through the directory the sidecar already mounts and adds
X-SelfPost-Filter, the HMAC-SHA256 of the message's queue id, hex;
a header of that name from the sender is removed.
- internal/milter/inbound.go: the verdict headers are kept as they
are read, and at end-of-message - when the queue id is known - they
count only if the signature fits (FilterSignature, hmac.Equal). No
key, no queue id, no signature or a wrong one: the row is that of
mail nobody judged (accept, selfpost, no detail).
The signature goes on to the upstream with the mail and is of no use
there: it fits one queue id.
Tried in a throwaway rspamd 3.11 container on the test server before
the Go side was written: the routine loads, signs
(2aa1ca6d... for key 0123...cdef and queue id 4A1B2C3D5E, the value
python's hmac gives and TestFilterSignatureIsWhatTheFilterWrites
pins), removes a sender's header of the same name, and adds nothing
without a queue id.
Tests: signed, unsigned, made-up, another message's, another key's,
the sender's followed by the real one, the next message on the
connection, no queue id; the key made once, read after, replaced when
damaged, left alone by the lists. e2e: filter.key is there, 644, 65
bytes.
docs/security.md: the accepted risk is replaced by a narrower one (the
key is readable on the host); Mail path describes the signature.
Checked on the test server, uncommitted tree: go vet ./... ok,
go test ./... ok (22 packages), make e2e ok.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
SelfPost
Self-hosted SMTP relay with a web panel — one Docker image, no provider.
Postfix, OpenDKIM, and a small Go panel run together under supervisord; you
configure domains, DKIM keys, and SASL applications once, then point your apps
at the SMTP endpoint.
SelfPost sends mail straight to the internet from your own IP, with per-domain DKIM signing. No mailboxes or webmail. An optional inbound relay (backup-MX / forwarder on port 25) forwards to an upstream; it does not store mail.
For: operators who run their own VPS or home server and want a simple relay they control, without a third-party SMTP provider.
Key properties: one container, multi-domain DKIM, SASL per application, send log and DNS checks in the panel, encrypted backups.
Features
- Outbound SMTP (465/smtps; optional 587 submission) with per-domain DKIM signing
- Optional inbound relay on port 25 (backup-MX / forwarder; off by default)
- Optional DMARC aggregate report ingest on port 25 (off by default)
- In-panel Help: a page of topics, opened from the
?in the head of a box - Per-application client IP allow-list for SMTP AUTH (optional)
- Web panel grouped by mail direction — Overview, Outbound (domains, log, queue, DMARC reports), Inbound, Server (health, system log, backup, users, settings)
- Multi-domain relay — each SASL application is bound to one sending domain
- DNS status checks (PTR, SPF, DKIM, DMARC) with in-panel re-check
- Two-level rate limiting — IP backstop (Postfix), per-domain ceilings, and trusted-IP app overrides
- Full-server backup and single-domain export/import (optional password encryption)
- Single Docker image; production data in a
./databind mount (the quick start below uses a named Docker volume instead)
Documentation
| Document | Contents |
|---|---|
| Operator guide | Reverse proxy, environment variables, DNS, IP warmup, panel operations, rate limiting, backup/restore, ports, image tag |
| Product boundaries | Purpose, deployment assumptions, out-of-scope items, multi-domain model |
| Architecture | As-built technical design |
| Security design | Mandatory requirements, accepted risks, the CSRF ADR |
| Development | Building, testing, docs rules, model routing, commits |
| Roadmap | Open work (1.x+) — direction, not commitments |
| CHANGELOG | Release history |
Found a vulnerability? Do not open an issue — SECURITY.md has the private reporting channel and the scope.
Repository: https://github.com/mixeme/selfpost — source, issues, releases, and
the ghcr.io/mixeme/selfpost image.
Requirements
Providing these is the operator's job — SelfPost cannot fix a blocked port or a missing PTR record for you. Details: Operator guide.
Platform
- Docker + Compose v2 on the host
- A reverse proxy in front of the panel (SelfPost never terminates HTTPS itself)
- Rough sizing: 1 vCPU, 512 MB–1 GB RAM, 8–10 GB disk (send log and
rotated
mail.logare the main growth drivers; both sit in the./datavolume, and both are capped — 90 days and 14 files by default)
Network and IP
- Static IP address
- Outbound TCP port 25 unblocked (many consumer/cloud hosts block it by default)
- PTR/rDNS for that IP pointing at your mail hostname (
SELFPOST_HOSTNAME) - Reasonable starting IP reputation — a fresh IP still needs warmup
Per sending domain
For every domain you add in the panel:
- SPF TXT record authorizing this server
- DKIM TXT record (value shown on the domain page)
- DMARC
_dmarcTXT record
See Domain-level DNS in the operator guide.
Per inbound domain (optional)
Only if you turn on inbound relay (INBOUND_RELAY_ENABLE=true):
- MX record pointing at
SELFPOST_HOSTNAME(keep any existing primary MX if this host is backup-MX)
See Inbound relay in the operator guide.
Quick start
First boot — create the admin account. On a fresh container SelfPost prints a one-time setup URL (valid ten minutes). Open it in a browser to choose the administrator username and password. Until you do, the panel has no login. Production deploy: Full deployment in the operator guide.
One container, panel at http://127.0.0.1:8080 — no reverse proxy, no TLS
files, no compose files. Good for clicking through the UI on your machine;
outbound mail will not reach the real internet without DNS, PTR, and port 25.
docker run --rm -d --name selfpost-try \
-p 127.0.0.1:8080:8080 \
-e SELFPOST_HOSTNAME=mail.local.test \
-e PANEL_COOKIE_SECURE=false \
-v selfpost-try-data:/data \
ghcr.io/mixeme/selfpost:2.0.1
Get the setup URL (pick one):
docker logs selfpost-try 2>&1 | grep -m1 'http'
docker exec selfpost-try cat /data/setup-token
The printed URL is https://mail.local.test/setup/<token>. For this local
trial rewrite it to http://127.0.0.1:8080/setup/<token> (same path token;
PANEL_COOKIE_SECURE=false so the cookie works over plain HTTP). Open it
before it expires.
When finished:
docker rm -f selfpost-try && docker volume rm selfpost-try-data
More detail (limitations, optional throwaway TLS for local SMTP): Local trial in the operator guide.
Reference deploy
Production layout: one docker-compose.yml, a .env, persistent ./data, and
TLS PEM files at ./certs (read by Postfix on 465/587). The panel is reached
only through a reverse proxy on 443 — port 8080 is bound to localhost in the
default compose file.
Full walkthrough — fetching the base files, setting up a reverse proxy and TLS (Apache/nginx/Caddy/Traefik), starting the container, and wiring up DNS — lives in the operator guide's Full deployment section, with proxy-specific commands under Reverse proxy.
The compose file always publishes 465, 587, and 25; Postfix listens
on 587 only when SUBMISSION_ENABLE=true, and on 25 when
INBOUND_RELAY_ENABLE=true and/or DMARC_REPORTS_ENABLE=true (see
Ports). Bump the
pinned image tag deliberately when upgrading, never :latest (why). Optional
variables (TRUSTED_PROXY_CIDR, rate limits, retention): see Environment
variables.
License
Copyright © 2026 Mikhail Yenuchenko.
AGPL-3.0. The AGPL closes the "SaaS loophole": if you run a modified version as a network-accessible service, you must make the modified source available to its users — not only when you distribute copies of the code. Third-party notices: NOTICE.