Last updated: 4 July 2026

These Terms of Use (“Terms”) govern your access to and use of the MailTester Ninja email verification service, including our website, widget and API (together, the “Service”), operated by Unlimited & Limited, 27 Old Gloucester Street, Holborn, London WC1N 3AX, United Kingdom (“we”, “us”, “our”). By subscribing to, accessing or using the Service, you agree to be bound by these Terms. If you do not agree, do not use the Service.

1. The Service

MailTester Ninja is a real-time email verification service. It checks whether an email address is likely deliverable by inspecting DNS records (MX) and performing a live SMTP conversation with the recipient mail server, without ever sending an actual email. Results are returned as a status (for example: accepted, rejected, catch-all, or undetermined).

The Service is privacy-first by design: we do not store, sell or share the email addresses you verify. Verification is performed at the DNS/SMTP level and only aggregate, non-personal metrics are retained. See our Privacy Policy & GDPR for details.

Because email infrastructure behaves unpredictably (greylisting, temporary failures, catch-all domains, provider-side anti-abuse controls), verification results are probabilistic indicators, not guarantees. See Section 9.

2. Accounts, API Keys and Subscriptions

Access to paid features is granted through an API key that is tied to your subscription. Your API key is personal and confidential. You are responsible for keeping it secret and for all activity carried out with it. If you believe your key has been compromised, contact us immediately.

You must provide accurate billing information and be authorised to use the payment method you supply. You must be at least 18 years old, or the age of majority in your jurisdiction, to use the Service.

3. Acceptable Use

You may use the Service only to verify email addresses that you have a legitimate reason to check — for example, validating addresses collected through your own opt-in sign-up forms, cleaning your own customer lists, or confirming an address at the point of entry. You must comply with all applicable laws, including anti-spam and data-protection laws (such as the UK GDPR, EU GDPR and the US CAN-SPAM Act).

4. Prohibited Uses

You must not, and must not allow anyone else to:

  • Directory harvesting / dictionary attacks — submitting generated, guessed, sequential or otherwise fabricated addresses in order to discover which ones exist on a domain.
  • Verify purchased, scraped, rented or otherwise non-consented email lists, or use the Service to enable the sending of unsolicited bulk email (spam), phishing or malware.
  • Use the Service to harass, defraud, or target individuals, or for any unlawful, deceptive or harmful purpose.
  • Circumvent, disable or exceed rate limits or plan quotas; share, resell, sublicense or redistribute the Service or your API key without our written consent.
  • Reverse-engineer, scrape, or attempt to derive the underlying methods of the Service, or interfere with its normal operation.

5. Fair Use, Rate Limits and Automated Abuse Protection

Each plan includes a daily verification allowance and per-connection rate limits, published on our pricing and API pages. You are responsible for keeping your request rate within those limits.

Automated integrity protection. The Service continuously and automatically monitors the quality of the verifications performed by each API key. An API key that produces an abnormally high proportion of invalid, undeliverable or rejected results — or exhibits patterns consistent with directory harvesting, scanning of non-consented lists, or other abusive behaviour — may be automatically and immediately suspended, with or without prior notice.

This protection is essential: abusive verification of bad lists rapidly damages the reputation of the shared mail infrastructure the Service relies on, which would degrade accuracy and availability for every other user. Suspension may be temporary and self-lifting, or, in cases of repeated or severe abuse, permanent. We may likewise suspend or restrict a key where we detect suspected fraud, payment disputes, or any breach of these Terms.

If you believe your key was suspended in error, contact our support team through our contact form; we review such cases individually and will restore access where appropriate.

6. Billing, Renewal and Cancellation

Paid plans are billed through our payment processor, Stripe, according to the plan and quantity you select. Subscriptions renew automatically for successive periods until cancelled. You can cancel at any time from your account or the Stripe billing portal; cancellation stops future renewals and your access continues until the end of the current paid period.

If a renewal payment fails, the subscription is cancelled and the associated key stops working. We do not store your card details — all payment data is handled directly by Stripe.

7. Refunds

If something isn’t right, contact us through our contact form. We deal with refund requests fairly and on a case-by-case basis, in accordance with applicable consumer-protection law.

8. Accuracy and Disclaimer of Warranties

The Service is provided on an “as is” and “as available” basis. We make reasonable efforts to return accurate results, but we do not warrant that verification is error-free or complete. In particular, catch-all domains cannot be definitively verified, and some mail servers return temporary or misleading responses. We do not guarantee deliverability of any message you subsequently send. You are responsible for how you use verification results.

9. Intellectual Property

The Service, including its software, brand, logo and content, is owned by us and protected by intellectual-property laws. These Terms grant you a limited, non-exclusive, non-transferable right to use the Service in accordance with them; no other rights are granted.

10. Limitation of Liability

To the fullest extent permitted by law, we will not be liable for any indirect, incidental, special or consequential damages, or for loss of profits, revenue, data or goodwill, arising out of or related to your use of (or inability to use) the Service. Our total aggregate liability for any claim relating to the Service shall not exceed the amount you paid to us for the Service in the three (3) months preceding the event giving rise to the claim. Nothing in these Terms excludes liability that cannot be excluded under applicable law.

11. Indemnification

You agree to indemnify and hold us harmless from any claims, losses or expenses arising out of your misuse of the Service or breach of these Terms, including any use that violates anti-spam or data-protection laws.

12. Suspension and Termination

We may suspend or terminate your access to the Service, in whole or in part, if you breach these Terms, misuse the Service, or where required to protect the Service or other users. You may stop using the Service at any time by cancelling your subscription.

13. Changes to these Terms

We may update these Terms from time to time. Material changes will be reflected by updating the “Last updated” date above. Your continued use of the Service after changes take effect constitutes acceptance of the revised Terms.

14. Governing Law

These Terms are governed by the laws of England and Wales, and the courts of England and Wales shall have exclusive jurisdiction over any dispute, without prejudice to any mandatory consumer-protection rights you may have in your country of residence.

15. Contact

Questions about these Terms? Reach us through our contact form and we’ll be happy to help.