MailTester Ninja gives you an email verification API and a web app that tell you whether an email address can actually receive mail, by asking the server that hosts it, right now. Fresh answers, not a lookup in an old database.

How a check works

1. The address is parsed and its syntax is validated.

2. The domain is resolved and its MX records are looked up.

3. MailTester Ninja opens an SMTP session with the recipient's mail server and stops at RCPT TO, so nothing is ever delivered to the person behind the address.

4. The server's answer is turned into a clear verdict, returned in about a second for most addresses.

What you get back

- ok: the mailbox exists and accepts mail (Accepted).

- ko: the address will bounce (Rejected, No MX) or is a throwaway inbox (Disposable).

- mb: uncertain, for example a catch-all domain that accepts every address, or a server that would not answer. We never turn an uncertain result into a false ok.

Ways to use it

- REST API: one GET request to /ninja?email=…&key=… on happy.mailtester.ninja returns JSON with the code and a reason.

- SDKs: official packages on npm (@mailtester-ninja/client) and PyPI (mailtester-ninja), typed and dependency-free.

- OpenAPI 3.1 spec: import it into Postman, Swagger, Power Automate or give it to an AI agent as a tool.

- No-code: step-by-step guides for n8n, Make, Zapier, Google Sheets and Clay.

- Web app: upload a CSV or paste addresses for bulk email verification, then export the results.

- Email finder: suggests someone's professional address when you know their name and their employer's domain.

Built for privacy

Each address is used for its check and then discarded, so your lists never become someone else's data, which is how we stay GDPR compliant.

Pricing without credits

- Free: key=free gives 10 API checks a day with no signup, a free token gives 50, plus free checks on the website.

- Starter: 100,000 checks every day for $6.99/week.

- Pro: the same 100,000 daily checks, billed $23.99/month.

- Ultimate: 200,000 daily checks at $39.99/month, and more on request.

Every plan renews its allowance daily, and you can stop whenever you want.

Who uses it

- Developers validating signups and checkout forms in real time.

- Sales and growth teams cleaning lead lists before cold outreach.

- Marketers protecting their sender reputation before a campaign.

- Agencies verifying contact data for several clients.

Teams that run their lists through it before a send see bounce rates under 1%. We would love feedback from the Peerlist community, especially on the API response format and on how catch-all domains should be reported.