craigmccaskill/posthorn — Self-hosted email gateway between your apps and a transactional mail provider (Postmark, Resend, Mai…

Description and use

**Brief summary**
Posthorn is a single‑container, Go‑based email gateway that sits between your applications and any transactional mail provider (Postmark, Resend, Mailgun, AWS SES, or an outbound SMTP server). It accepts inbound mail via three “ingress shapes” – an HTTP form, a REST‑style HTTP API, or raw SMTP – and forwards the messages to the configured provider, all driven by a tiny TOML configuration file.

**Value**

• **Unified interface**: Developers can switch providers or add a new one without changing application code, because Posthorn abstracts the provider’s API behind a consistent HTTP/SMTP endpoint.
• **Fast AI‑enabled prototypes**: By handling email delivery reliably, teams can focus on building AI features (e.g., RAG pipelines, agent notifications) without wrestling with provider‑specific quirks.
• **Low operational overhead**: One Docker image and a single config file make deployment trivial in any container‑orchestrated environment (Docker Compose, Kubernetes, Nomad, etc.).

**Practical adoption path**

1. **Deploy** – Pull the official Docker image, mount a TOML file with your chosen provider credentials, and run the container (or add it to your existing compose/k8s stack).
2. **Configure ingress** – Choose the appropriate ingress shape for your app (e.g., HTTP API for microservices, SMTP for legacy systems).
3. **Update your app** – Point your email‑sending code to the Posthorn endpoint; no code changes are needed for the underlying provider.
4. **Iterate** – Swap providers or add new ones by editing the TOML and restarting the container; no redeployment of the consuming services.

**Production readiness**

• **Activity & community**: 203 ★, recent commit (2026‑07‑04), 10 forks, and active issue discussions indicate a healthy maintainer base.
• **Stability**: The single‑binary, statically compiled Go binary reduces runtime dependencies; the Docker image is immutable and easy to version.
• **Observability**: Built‑in logging and health‑check endpoints make monitoring straightforward in production environments.
• **Risk considerations**: The license and security posture appear clean, but a final audit of the repository’s licensing terms and any disclosed vulnerabilities is advisable before a critical rollout.

Overall, Posthorn is a mature, low‑friction component that can be dropped into existing stacks to standardize email delivery while freeing developers to concentrate on higher‑level AI and business logic.

Problem

craigmccaskill/posthorn helps add AI capability without starting from a blank model stack.

Outcome

High for an OSS candidate: recent activity, adoption, and ecosystem signals are strong enough for a serious pilot.

Workflow

• prototype AI features
• build RAG or agent workflows
• evaluate model tooling

Evidence

Self-hosted email gateway between your apps and a transactional mail provider (Postmark, Resend, Mailgun, AWS SES, or outbound-SMTP). Three ingress shapes (HTTP form, HTTP API, SMTP). One Docker container, one TOML config.

Source