Syntax, DNS/MX, live SMTP handshake, catch-all detection, 1M+ disposable registry, role-based flags and typo suggestions — in one sub-second check. 20 verifications/min free. No signup.
RFC-5321 syntax, MX lookup with A/AAAA fallback, retry on tempfail.
EHLO/MAIL FROM/RCPT TO against the primary MX with MX fallback & deadline.
Composite 0-100 score, A–F grade, catch-all and role-based flags, typo suggestion.
| Status | Meaning | What to do |
|---|---|---|
| valid | Inbox exists, mail will accept. | Send safely. |
| risky | Catch-all / role-based / suspicious pattern. | Send but monitor bounces. |
| invalid | Mailbox rejected, disposable, or bad syntax. | Remove from list. |
| unknown | Greylisted / temp fail. | Retry in 15 min. |
test@gmial.com → invalid · suggestion: test@gmail.comadmin@somecompany.com → risky · role-basedjunk@mailinator.com → invalid · disposablexqzabc998877@example.com → risky · likely random localsundar@google.com → risky · catch-all domainYes. 20 free checks/minute/IP, no signup. Paid plans raise the limit and add batch cleaning.
~98% for normal domains. Catch-all domains always accept, so we flag them as risky rather than valid.
A composite of syntax, DNS, SMTP, catch-all, role-based, disposable and MX-health checks — mapped to a letter grade A–F.
No. The single validator is stateless. For paid batch cleaning, files are processed in memory and deleted within 24h.
We compare the domain to a list of ~60 common providers using Levenshtein distance. gmial.com → gmail.com.
Yes. POST /api/validate-email or see our Email Verification API. Grab an API key from your dashboard for raised limits.
Any HTTP client: cURL, fetch, requests, axios, Guzzle. See API docs.
Starter ($19 for 10k) and Growth ($49 for 50k) cover bulk and API verification.
When you verify a single email address in real time — whether through our web inspector above or via POST /api/v1/verify-single — KaijuVerifier executes a 7-stage diagnostic sequence in ~180ms without ever transmitting an actual message to the recipient’s inbox.
After validating RFC 5322 grammar, decoding IDN punycode, checking Levenshtein typo distance against 150+ consumer ISPs, and querying our 112,000+ disposable domain graph, our resolver fetches the domain’s authoritative MX records. It then opens a TLS 1.3 socket to the lowest-priority MX server, sends EHLO and MAIL FROM, probes a randomized canary address to detect domain-wide Catch-All behavior, and evaluates the exact 250, 450, or 550 response to RCPT TO before issuing QUIT.
| SMTP Handshake Step | Wire Protocol Command | Diagnostic Interpretation |
|---|---|---|
| Step 1: Socket & Banner | TCP 25 Connect → 220 mx.host ESMTP + STARTTLS (TLS 1.3) | Confirms mail server reachability & fingerprints MTA software |
| Step 2: Canary Catch-All Probe | RCPT TO:<kv-canary-9f8a2@domain.com> | If 250 OK → Domain is Catch-All; triggers entropy risk scoring |
| Step 3: Target Mailbox Probe | RCPT TO:<target.user@domain.com> → QUIT | 250 OK = Valid · 550/554 = Invalid · 421/450 = Greylisted Retry |