VaultSandbox – Test your real MailGun/SES/etc. integration
I've spent the last few months working on something I wish I'd had years ago. I kept running into the same issue: CI green, production mail broken. TLS handshake failures, DKIM alignment mismatches, SPF soft-fails ... the stuff that only surfaces when real mail servers are involved. Most test tools (Mailpit, MailHog) are catch-alls. They confirm "an email was sent" but don't validate the protocol. They also aren't designed for network-exposed environments: no auth, unprotected Web UI, easy to enumerate messages. VaultSandbox is my attempt at fixing that. It's a self-hosted SMTP gateway…
VaultSandbox – Test your real MailGun/SES/etc. integration launched on January 6, 2026 with 58 votes, #514 of 14,584 launches that month and more than 95% of that year's launches.
In plain words
VaultSandbox is a self-hosted SMTP gateway that validates email protocol standards like SPF, DKIM, DMARC, and rDNS during testing. It's built for developers who need to catch mail delivery issues before production, allowing them to test against real email providers like SES and SendGrid without changing application code. Unlike generic catch-all tools, it validates actual protocol compliance and includes authentication and security features suitable for network-exposed environments. It offers client SDKs for Node, Python, Go, Java, and .NET, plus a Web UI and CLI.
written from the facts on this page · September 2026
From the sources
Keep your provider and your config. Just swap the recipient to validate real TLS, DNS, and SPF/DKIM entirely inside your VPC. Works with Postmark, SendGrid, SES, and more.
Self-hosted SMTP testing gateway with real TLS, DNS, authentication, spam scoring, and chaos engineering. No mocks, no polling, no flaky tests. Works with SendGrid, Postmark, SES, and more.
VaultSandbox is a self-hosted, receive-only SMTP testing gateway that behaves like a real SMTP server — including TLS, DNS, authentication, spam filtering/scoring, and failure modes — so your tests stop lying to you. You don't need to set up DNS or TLS to get started. Perfect for air-gapped or offline development. # docker-compose.yml services : vaultsandbox : image : vaultsandbox/gateway:latest ports : - '127.0.0.1:2525:25' - '127.0.0.1:8080:80' volumes : - vsb_data:/app/data volumes : vsb_data : View localhost docs docker-compose.yml Copy # docker-compose.yml services : vaultsandbox : image : vaultsandbox/gateway:latest ports : [ "25:25" , "80:80" , "443:443" ] environment :…from vaultsandbox.com
In the maker’s words, at launch
I've spent the last few months working on something I wish I'd had years ago. I kept running into the same issue: CI green, production mail broken. TLS handshake failures, DKIM alignment mismatches, SPF soft-fails ... the stuff that only surfaces when real mail servers are involved. Most test tools (Mailpit, MailHog)…
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