Email Verifier (SMTP, MX, Catch-All) MCP server

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Bulk Email Verification API — for n8n, AI Agents & MCP

Verify email addresses in bulk: RFC 5322 syntax → DNS/MX → disposable, role and free-provider lists → a live SMTP handshake with a mandatory catch-all probe. No email is ever sent — the check opens an SMTP session, reads the reply codes and hangs up.

➜ Try it on Apify

{
  "email": "john@example.com",
  "status": "deliverable",
  "sub_status": "valid_mailbox",
  "score": 100,
  "checks": {
    "syntax": true, "domain_exists": true, "mx_found": true,
    "smtp_connectable": true, "mailbox_exists": true, "catch_all": false,
    "disposable": false, "role_based": false, "free_provider": false,
    "a_record_fallback": false, "has_tag": false
  },
  "mx_record": "aspmx.l.google.com"
}

Why pipelines like it

Most verifiers are written for a human reading a dashboard. This one assumes the caller is code.

That changes what the output has to guarantee:

1. status is always one of four values. deliverable, undeliverable, risky, unknown. Never null, never empty, never a fifth value. Enumerate them once and stay correct.

2. All eleven checks keys are present on every record. A check that never ran is false, and the reason lives in sub_status. Nothing disappears.

3. Catch-all domains and Gmail-type providers are reported honestly. They come back risky with a reason, not a fabricated "valid".

Those three together mean you write this:

const mailable = results.filter(r => r.status === 'deliverable');
const neverSend = results.filter(r => r.status === 'undeliverable' || r.checks.disposable);
const retryLater = results.filter(r => r.status === 'unknown');

and not this:

const mailable = results.filter(r => r?.status === 'valid' && (r.checks?.catch_all ?? false) === false);

The second line is what every nullable-by-default API forces on you. It matters more for an agent than for a person: an agent cannot write ?? false — it acts on what it reads. A field that sometimes vanishes is not an inconvenience, it is a wrong answer delivered with confidence.

What to do with each result

Full table with scores and reasoning: docs/statuses.md

The distinction that matters: undeliverable means we found out it is dead; unknown means we could not find out. Tools that merge the two report better-looking numbers and quietly delete real customers from your list.

Use it in n8n

Shortened. The full README is on GitHub.