mixandClaude Opus 5.5
c171fb5bc7
A message's From: line is held against the application that sends it, under the rule Postfix holds the envelope sender to. OpenDKIM chooses the key by that line, so until now an application could have mail signed as another domain of the server or as the server itself. The check (internal/milter/sender.go) - A role of the panel on a socket of its own (SENDER_CHECK_SOCKET), first in smtpd_milters and strict: default_action=tempfail. The journal milter keeps its socket and stays fail-open. postfix-wrapper waits for the new socket. - It reads no database: what an application may send as comes from Postfix's own sender_login_maps, what the server signs for from OpenDKIM's SigningTable. Both are read again when they change; one that cannot be read defers mail. - One From: field, one address, allowed by the envelope's lookup; then no other name of the SigningTable may appear anywhere in the raw line. Refused: 550 5.7.1 naming the line, reduced to printable ASCII. - A refusal is a send-log row with reason "from" and the header address (migration 0006), written by another goroutine and not waited for. The journal's refusals record their reason too (limit, client), and the notifier takes only a limit's. What it costs (docs/plans/from-header-binding.md, Statistics) - The role marks itself alive every 2 s; at start the gap since the mark is downtime, counted from Postfix's start if later and not at all when supervisord says Postfix is not running. - The log tailer counts the connections Postfix turned away: a warning that names the socket, then milter-reject "Service unavailable" from the same smtpd. Seen on the stand: the client is refused from CONNECT on and leaves at AUTH (454), so no MAIL line is ever written. - sender_check_days, a row per UTC day, kept a year. Pages - Health: the card "Sender check", the socket's row, and the cards layout - boxes numbered by importance in two stacks read in rows; the left stack polls, the three readings of the right one are swapped in by id. - Outbound log: a refused row says why in its tag (wrong From, wrong client, rate-limited); the message's page shows the From: line and what the application may send as. - Help: topic "Sender check", word for word the mockup's. Found by the stand, fixed here: the names for the second look came from the sender bindings, and a domain with a key and no application yet was not among them. e2e: negative_journal_milter_fail_open is gone - it proved that mail passes with the panel down, which is no longer so. In its place sender_check_holds_the_from_line (another domain's From:, the hostname's, a stranger's, an address off the list, another sender in the display name - refused; own addresses - delivered) and panel_down_defers_mail (4xx with the panel stopped, the container alive, mail again after, downtime and one deferred message on Health, the card warning). Test server, this tree before the last cosmetic edits (a fixture row, a fact's size, docs): go vet ok, go test 23 packages ok, make e2e ok (337 s). Locally after them: internal/web/view 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:2.3.0
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.