# Posthorn

> **TL;DR.** Posthorn is a self-hosted email gateway that centralizes transactional mail delivery across all your apps into one Docker container.

- **Category:** Developer Tools / Infrastructure / Email
- **Stage:** nascent
- **Age:** 7 days
- **Origin date:** 2026-05-27
- **First detected:** 2026-05-27
- **Canonical URL:** https://earlyterms.com/term/posthorn
- **Sources:** 4 primary URLs

## Definition

Posthorn is a self-hosted email gateway that centralizes transactional mail delivery across all your apps into one Docker container. Instead of wiring each app to Postmark, Resend, Mailgun, or AWS SES independently, every app points at Posthorn, which holds the credentials and routes outbound mail.

Created by Craig McCaskill and [released as v1.0.0 on May 26, 2026](https://github.com/craigmccaskill/posthorn/releases/tag/v1.0.0), Posthorn accepts three ingress shapes — HTTP form, JSON API, and SMTP — so legacy apps like Ghost, Gitea, and Mastodon slot in without modification. The entire system ships as a single 10 MB Go binary or Docker image configured by one TOML file.

## Analogy

Think of it as a shared postal counter for every service you run — one desk, five couriers.

## Why it's emerging now

As self-hosters run more apps per server (Ghost, Gitea, Mastodon, custom APIs), the friction of managing separate transactional mail integrations per app compounds. Posthorn's v1.0.0 launch on May 26, 2026 and same-day HN post crystallized the category name for a long-standing infrastructure gap: a sidecar that handles credentials, rate limiting, and provider routing once for every app.

## Related terms

- *related:* agent-email
- *competitor:* Postal
- *competitor:* Nullmailer
- *related:* Resend
- *related:* Postmark
- *related:* Mailgun
- *related:* AWS SES
- *parent:* Docker sidecar
- *related:* webhook-secrets
- *parent:* transactional email

## Sources

1. [craigmccaskill/posthorn — GitHub repository (v1.0.0, May 26, 2026)](https://github.com/craigmccaskill/posthorn)
2. [Posthorn — official site and documentation](https://posthorn.dev/)
3. [Show HN: Posthorn, self-hosted mail without the mail server (60 pts, 43 comments)](https://news.ycombinator.com/item?id=48289624)
4. [Posthorn v1.0.0 — Initial release notes (May 26, 2026)](https://github.com/craigmccaskill/posthorn/releases/tag/v1.0.0)

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_Generated by EarlyTerms · https://earlyterms.com/term/posthorn_