Posthorn, self-hosted mail gateway

Hacker News

Introducing Posthorn, a self hosted email gateway. One docker container (or Go binary) between every self hosted app on your VPS and your transactional email provider. Set up Posthorn once, point your apps to it, done. I was trying to deploy Ghost on a DigitalOcean droplet and found that DO and many different VPS services have started to block the default SMTP ports to try to combat the various types of abuse they get. To actually configure my app, I had to hack together a Postfix relay. In another project, I had a static site which had a contact form, but my free Formspree account was occasionally hitting usage limits and I desperately wanted some of the anti-spam features they had gated behind their paid accounts so I put together a caddy module to catch HTTP POSTs and bounce them to my provider. I kept bumping into these same email issues. Many of the services I wanted to host (Gitea, Mastodon, Umami, Comentario) ran into the same limitations. This felt like a really common issue that had no good solution. Posthorn is what I built to solve this. It's a small Go binary (or 10 MB docker image) that sits between your self hosted apps and your transactional email provider of choice (shipping with support for Postmark, Resend, Mailgun, Amazon SES or an outbound SMTP relay). It also accepts POSTs from HTML forms to support static site needs while adding security layers such as honeypot fields, origin checks and IP rate limiting. There's also a JSON HTTP API that supports Bearer auth for backend scripts or cron jobs that just want a /send endpoint. I now use this personally in multiple scenarios and I've spent a lot of time beating this up and testing against what I can validate. I'd love to hear how this might be useful for you, what breaks and any feedback you might have. It's open source under Apache 2.0 and I'd love contributions. I'm planning to support and grow this for the long haul. Code: https://github.com/craigmccaskill/posthorn Docs: https://posthorn.dev/ Longer write up: https://craigmccaskill.com/introducing-posthorn/ Previous HN discussion on the exact issue I'm trying to solve: https://news.ycombinator.com/item?id=43620318

Visit product View on Hacker NewsMay 27, 2026

Share card

Actual performance

83points

60comments

Made the leaderboard

Launch Intel predictions

Analyze your own launch →

Indie HackersFits the IH revenue-focused audience · Strong signals: supports, started, ios · Missing: reddit linkedin, podcasting, created

87%87% predicted probability of success on Indie Hackers, based on ML models trained on real launch data.

best fitHighest predicted score across all platforms for this description.

Hacker NewsStrong engagement from HN community · Strong signals: open source, ide, io · Missing: https docs, excited, just released

65%65% predicted probability of success on Hacker News, based on ML models trained on real launch data.

nativeThis product was originally launched on this platform.

Product HuntOn track for Day 1 leaderboard · Strong signals: apps, dock, new · Missing: mac, agents, macos

57%57% predicted probability of success on Product Hunt, based on ML models trained on real launch data.

TrustMRRLess likely to generate early MRR · Strong signals: ios, personal, apps · Missing: mobile apps, entrepreneurs, video

47%47% predicted probability of success on TrustMRR, based on ML models trained on real launch data.

AppSumoMay struggle as an AppSumo deal · Strong signals: host, occasional · Missing: plus, platform, intuitive

30%30% predicted probability of success on AppSumo, based on ML models trained on real launch data.

Acquire.comPre-revenue stage for this audience · Missing: arr, mrr, revenue

17%17% predicted probability of success on Acquire.com, based on ML models trained on real launch data.

BetaListMay not resonate with beta-testers · Strong signals: paid · Missing: web3, chat, crypto

0%0% predicted probability of success on BetaList, based on ML models trained on real launch data.

Correct prediction on native model

Similar products

Iframely - self-hosted embeds gateway (MIT)65%Launch Intel prediction score: how likely this product is to succeed on its source platform, based on its name, tagline, and description.

Iframely - self-hosted embeds gateway (MIT)

Hacker News3

Mantis, A self-hosted LLM gateway58%Launch Intel prediction score: how likely this product is to succeed on its source platform, based on its name, tagline, and description.

Mantis, A self-hosted LLM gateway

Hacker News5

Instanote – self-hosted pinboard68%Launch Intel prediction score: how likely this product is to succeed on its source platform, based on its name, tagline, and description.

Instanote – self-hosted pinboard

Hacker News8

Mob – Self Hosted Polling67%Launch Intel prediction score: how likely this product is to succeed on its source platform, based on its name, tagline, and description.

Mob – Self Hosted Polling

Hacker News2

Mob – Self Hosted Polling67%Launch Intel prediction score: how likely this product is to succeed on its source platform, based on its name, tagline, and description.

Mob – Self Hosted Polling

Hacker News12

Self-Hosted Literate K3s Cluster60%Launch Intel prediction score: how likely this product is to succeed on its source platform, based on its name, tagline, and description.

Self-Hosted Literate K3s Cluster

Hacker News1

A Self-Hosted Podcatcher68%Launch Intel prediction score: how likely this product is to succeed on its source platform, based on its name, tagline, and description.

A Self-Hosted Podcatcher

Hacker News2

Self hosted x86-64 assembler75%Launch Intel prediction score: how likely this product is to succeed on its source platform, based on its name, tagline, and description.

Self hosted x86-64 assembler

Hacker News4

Self Hosted WebSocket Filesharing74%Launch Intel prediction score: how likely this product is to succeed on its source platform, based on its name, tagline, and description.

Self Hosted WebSocket Filesharing

Hacker News4

Self-hosted Thunderclap68%Launch Intel prediction score: how likely this product is to succeed on its source platform, based on its name, tagline, and description.

Self-hosted Thunderclap

Hacker News2

Browse all products Analyze your launch