@lacspace/email-verify

Does this mailbox actually exist? — best-effort deliverability checks (MX + SMTP probe).

Goes one step past syntax: resolves the domain's MX records and (optionally) runs a real SMTP RCPT TO probe to ask the receiving server whether the mailbox exists — without ever sending a message. Built on Node's dns + net.

• 🔎 Syntax + disposable (via @lacspace/email-validate)
• 📇 MX record lookup, sorted by priority
• 📡 Optional SMTP RCPT probe → deliverable / undeliverable / unknown
• 🚫 No email is ever sent
• 🟢 Node 18+ · zero npm dependencies (only our own email-validate)

⚠️ Read this. Live SMTP verification is inherently unreliable. Many mail servers greylist, use catch-all (accept every address), or block probes outright — so unknown is common and a positive means "likely deliverable", never a guarantee. Outbound port 25 is also blocked on many hosts (incl. most serverless/PaaS). Use it to catch obvious typos and dead domains, not as a hard gate.

Install

npm install @lacspace/email-verify      # or pnpm add / yarn add / bun add

Usage

import { verifyEmail } from "@lacspace/email-verify";

await verifyEmail("[email protected]");
// {
//   email: "[email protected]",
//   valid: true,
//   syntax: true,
//   disposable: false,
//   role: false,
//   mxFound: true,
//   mxRecords: [{ exchange: "gmail-smtp-in.l.google.com", priority: 5 }, …],
//   smtp: "unknown"   // Gmail greylists probes — expected
// }

// MX-only (fast, reliable, no port-25 needed) — great default in cloud/serverless
await verifyEmail(email, { checkSmtp: false });

Lower-level helpers

import { resolveMx, smtpCheck } from "@lacspace/email-verify";

await resolveMx("lacspace.com");
// [{ exchange, priority }, …] (sorted best-first; [] if none)

await smtpCheck("[email protected]", "mx.example.com", { timeout: 8000 });
// "deliverable" | "undeliverable" | "unknown"

Options

| Option | Default | Description | | --- | --- | --- | | checkSmtp | true | run the live RCPT probe (set false for MX-only) | | fromAddress | verify@<hostname> | MAIL FROM used in the probe | | timeout | 10000 | per-connection timeout (ms) | | extraDisposable | — | extra throwaway domains |

The Lacspace MailKit

| Package | For | | --- | --- | | @lacspace/mailer | Send email over SMTP | | @lacspace/email-templates | Build responsive HTML emails | | @lacspace/email-validate | Validate & normalize addresses | | @lacspace/email-verify | MX + SMTP deliverability checks (this package) |

Licensing

This package is free under the Lacspace Free Licence — MIT-equivalent freedoms. Use it in personal and commercial projects at no cost; just keep the notice.

Not every Lacspace package is free. We also offer Commercial (paid), Client-specific, and Private (proprietary) packages under separate terms. See the full Lacspace Licence Centre.

Part of the Lacspace ecosystem — 35 zero-dependency, isomorphic TypeScript packages.

All packages ↗ · npm org ↗ · Licence Centre ↗ · GitHub ↗