We make email debuggable
SMTPTester was built by engineers who spent too many late nights staring at vague "could not send mail" errors. We thought the world deserved a better diagnostic tool. So we built one.
Our story
SMTPTester started as an internal tool. Our team was running a SaaS product whose password-reset emails kept silently failing for a small subset of customers. Every existing online SMTP checker either ran a glorified DNS lookup or required us to paste credentials into a sketchy form with no obvious privacy guarantees. So we wrote our own — a real protocol walker that returned the raw 220, 250, and 535 codes from the server and explained them in plain English.
Over the following months it became the tool we reached for every time a deliverability question came up. We open-sourced the diagnostic engine, polished the UI, and put it online for free because the world has enough opaque email infrastructure already. Today SMTPTester is used by developers at startups, agencies running campaigns for enterprise clients, and IT administrators keeping internal mail systems healthy.
What we believe
Diagnostics over guesswork
Every test should answer "what is broken and how do I fix it?" — not just "yes/no".
Privacy by default
Your credentials are never written to disk, logs, or analytics. Period.
Free for everyone
Email infrastructure should not gatekeep developers. The core tester will always be free.
Plain-English explanations
Protocol jargon is fine when it helps. The summary should be readable by your CEO.
Who uses SMTPTester
- Developers debugging transactional email integrations.
- Marketing teams verifying provider migrations before a campaign goes out.
- SaaS founders figuring out why password resets are not landing.
- IT administrators validating internal Postfix and Exchange configurations.
- Agencies auditing client SMTP setups before taking over deliverability.
Try the tool
It is free, requires no signup, and gives you results in under ten seconds.
Run a free SMTP test