Vault Sandbox
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Welcome to VaultSandbox

VaultSandbox just hit version 0.9.1, and this feels like the right time to start writing.

What is VaultSandbox?

VaultSandbox is a self-hosted SMTP testing gateway. Most email testing tools are mock servers. They confirm an email was “sent” but miss the failures that actually happen in production: TLS negotiation, SPF/DKIM/DMARC validation, greylisting, or random SMTP errors.

VaultSandbox is a real SMTP gateway (not a mock) that you can run locally for quick testing or deploy to a public IP to receive real emails from providers like SendGrid or SES.

The journey so far

I originally built VaultSandbox for production-realistic testing. Localhost worked, but I didn’t give it much attention. I assumed most people would want the “real” setup first.

I was wrong. Most devs just want something that works on localhost before thinking about production realism.

So I overhauled the local experience. You can run it with Docker, point your app at it, and write deterministic tests using the SDKs. Features like email authentication (SPF/DKIM/DMARC) are optional since they need a real server anyway. Start simple, scale when you need to.

Where we are now

Version 0.9.1 has all the core features implemented:

  • Works on localhost out of the box, no config required
  • Chaos mode per inbox: simulate greylisting, dropped connections, latency, specific error codes
  • Webhooks (global and per inbox) with filtering, plus spam scoring via rspamd
  • SDKs for deterministic tests
  • Optional email authentication and TLS, toggle per inbox

The code is stable, the features are there. What’s missing is real-world validation.

Why not 1.0 yet?

I need feedback. I need people to use it, break it, and tell me what’s missing. There are probably features I haven’t thought of, edge cases I haven’t hit, and bugs that only show up in real environments.

That’s where you come in.

Get involved

If you’re tired of flaky email tests or want to catch delivery issues before production, give VaultSandbox a try.

If you find it useful, a star on the repo helps more than you’d think.

Let’s get to 1.0 together.