Project

Changelog

All notable changes to this project are documented here. The format follows Keep a Changelog and the project uses Semantic Versioning.

#Unreleased

Install instructions for the release packages: one-step .deb and .rpm installs for amd64 and arm64, a binary-only install, checksum verification, and upgrade and uninstall steps.
Container docs list the image tags (X.Y.Z, X.Y, latest).
The docs site build fails when an install command or image tag points at an older release than the latest one in this changelog.
Release checksums and container images are signed with cosign (keyless), and archives, packages and images carry build provenance attestations. See SECURITY.md for verification.

Examples use the 0.1 image tag instead of latest.
The sendmail symlink instructions work with the packages and no longer need a source checkout.
Building from source needs Go 1.27 or newer.
A message that gives a checked field (From, To, Cc, Bcc, HtmlBody, TextBody, TemplateId, TemplateAlias, MessageStream) more than once, under any capitalization, or a template batch with more than one Messages, is rejected with 422 instead of resolved unpredictably.
A response from Postmark that is not valid JSON is no longer relayed with its own content type; the API answers 502 with a JSON error instead. JSON responses keep their status and are written compactly with a trailing newline.

The container image reports its version without a v prefix, matching the binaries and packages.
A field holding only Unicode whitespace such as a non-breaking space now counts as blank whether or not it is JSON-escaped, so the default From applies and an empty required field is rejected.
Whitespace-only defaults and stream overrides (?stream=%20, a blank X-Postmarkd-Stream) are ignored instead of being sent as a blank MessageStream, and defaults are trimmed.

The first release: a small daemon that lets anything on a host or in a pod send mail through Postmark.

Postmark-compatible HTTP API: /email, /email/batch, /email/withTemplate and /email/batchWithTemplates. Existing Postmark SDKs work by changing their base URL.
SMTP server (POSTMARKD_SMTP_LISTEN) that converts MIME mail, including attachments, inline images and Postmark's X-PM-* headers.
sendmail compatibility: invoke the binary as sendmail and cron, mail, PHP mail() and friends deliver through Postmark.
postmarkd send for scripts: bodies from stdin or files, attachments, templates, streams, tags and metadata.
Default From and MessageStream, plus per-request stream selection (?stream=, X-Postmarkd-Stream).

Validation before Postmark sees a message; original bytes are forwarded untouched.
Pooled upstream connections, a concurrency limit, and retries only when Postmark cannot have accepted the message (no duplicate mail).
Optional async mode with a bounded in-memory queue, back-pressure and graceful drain on shutdown.

TCP and unix socket listeners (several at once), systemd socket activation (including SMTP on port 25 via postmarkd-smtp.socket), sd_notify readiness and watchdog, and a hardened unit.
Optional client token authentication; the Postmark token can be loaded as a systemd credential.
Prometheus metrics, /healthz and /readyz; postmarkd healthcheck.
postmarkd check-domain checks DKIM, Return-Path (SPF alignment) and DMARC records.
Blackhole mode (POSTMARKD_BLACKHOLE) for tests, with captured mail at /blackhole/messages.

Linux binaries, .deb and .rpm packages for amd64 and arm64, and a multi-arch distroless container image at ghcr.io/rossedman/postmarkd.
Docker Compose, Kubernetes sidecar and GitHub Actions examples.
Documentation site at https://rossedman.io/postmarkd/.
Benchmarks for every component, run in CI with a regression gate.