Test Methodology

MailSentry vs ZeroBounce — March 19, 2026

Objective

Compare the accuracy and classification of MailSentry and ZeroBounce on the same set of emails, tested at the same time, under the same conditions. No cherry-picking, no retries, no post-hoc adjustments.

Email Selection

We selected 10 emails covering every major validation category a real-world list would contain:

  1. Valid corporate — ceo@apple.com
  2. Valid free provider — a real Gmail address
  3. Disposable — test@guerrillamail.com
  4. Role-based — info@google.com
  5. Typo — john@gmial.com (misspelled gmail.com)
  6. Catch-all — hello@zapier.com
  7. Bad syntax — not-an-email
  8. Fake mailbox — randomxyz123abc@microsoft.com
  9. Gibberish — asdfjkl@yahoo.com
  10. Spam trap / suppression — test@mailinator.com

Emails were chosen to stress-test edge cases, not to favor either service. Both services had categories where they performed better (MailSentry on gibberish, ZeroBounce on SMTP verification).

Test Procedure

  • All 10 emails were submitted to both services within a 60-second window on March 19, 2026.
  • ZeroBounce was tested via their bulk validation dashboard with Verify+ enabled for maximum accuracy.
  • MailSentry was tested via the production API at api.mailsentry.dev/v1/verify.
  • Each email was tested exactly once. No retries or re-runs were performed.
  • Results were recorded as-is from each service's response — no manual overrides.

Scoring Criteria

Each email was evaluated on whether the service returned a useful, correct classification:

  • Correct — the service identified the email's issue (or confirmed it as valid) accurately.
  • Winner — if one service provided a more specific or accurate result, it won that test. If both were equally correct, it was scored as a tie.

Final score: MailSentry 9/10, ZeroBounce 9/10. 8 ties, 1 MailSentry win (gibberish detection), 1 ZeroBounce win (SMTP verification on Microsoft).

Where ZeroBounce Won

Test #8 (randomxyz123abc@microsoft.com): ZeroBounce correctly returned "invalid (mailbox_not_found)" while MailSentry returned "risky (suspicious)" with a score of 35. ZeroBounce has stronger SMTP verification for providers like Microsoft that block standard SMTP checks. We acknowledge this openly.

Where MailSentry Won

Test #9 (asdfjkl@yahoo.com): MailSentry flagged this as "invalid (gibberish)" using its built-in gibberish detection algorithm (bigram analysis, vowel ratios, consonant runs). ZeroBounce returned "invalid (mailbox_not_found)" — correct via SMTP, but without identifying why the address is bad. If SMTP had been inconclusive, ZeroBounce would have had no fallback. MailSentry would still catch it.

Limitations

  • 10 emails is a small sample. Results may differ at scale or with different email types.
  • SMTP verification results can vary depending on the time of day, server load, and provider rate limits.
  • ZeroBounce offers features not tested here (e.g., activity scoring, abuse detection).
  • This test was conducted by MailSentry. We have an inherent bias, which is why we publish the full methodology and acknowledge where ZeroBounce outperformed us.

Raw Data

Full results for all 10 emails — including MailSentry scores, ZeroBounce classifications, and winner determinations — are published on the comparison page. If you have questions about this test or would like to request a retest, contact us at hello@mailsentry.dev.