Email Verifier

A simple, zero-runtime-dependency email verification library for Node.js. Verify email addresses through format validation, DNS checking, and SMTP probing.

Features

• Format Validation - RFC 5322 compliant email format checking
• DNS Verification - MX record lookup with A record fallback
• SMTP Probing - RCPT TO verification without sending email
• Catch-all Detection - Identifies domains that accept any email
• Provider Detection - Identifies mail providers (Google, Microsoft, etc.)
• Caching - Built-in caching for performance
• Rate Limiting - Token bucket throttling with exponential backoff
• Zero Dependencies - Uses only Node.js built-ins at runtime

Installation

npm install email-verifier-check

CLI Usage

# Verify a single email
npx email-verifier-check check [email protected]

# Verify multiple emails
npx email-verifier-check check [email protected] [email protected]

# Output as JSON
npx email-verifier-check check [email protected] --json

# Skip SMTP check (faster, less accurate)
npx email-verifier-check check [email protected] --no-smtp

# Skip catch-all detection
npx email-verifier-check check [email protected] --no-catchall

Programmatic Usage

import { verifyEmail, verifyEmails } from "email-verifier-check";

// Verify a single email
const result = await verifyEmail("[email protected]");

console.log(result);
// {
//   email: '[email protected]',
//   valid: true,
//   confidence: 0.95,
//   details: {
//     formatValid: true,
//     mxRecords: ['aspmx.l.google.com'],
//     smtpStatus: 'accepted',
//     catchAll: false,
//     provider: {
//       name: 'Google Workspace',
//       url: 'https://workspace.google.com'
//     }
//   }
// }

// Verify multiple emails
const results = await verifyEmails(["[email protected]", "[email protected]"]);

Options

interface VerifyOptions {
  // Timeout for DNS lookups in milliseconds (default: 5000)
  dnsTimeout?: number;

  // Timeout for SMTP connections in milliseconds (default: 10000)
  smtpTimeout?: number;

  // Whether to perform SMTP verification (default: true)
  smtpCheck?: boolean;

  // Whether to perform catch-all detection (default: true)
  catchAllCheck?: boolean;

  // The sender email to use in SMTP MAIL FROM (default: [email protected])
  senderEmail?: string;

  // SMTP port to connect to (default: 25)
  smtpPort?: number;
}

// Example with options
const result = await verifyEmail("[email protected]", {
  smtpTimeout: 15000,
  catchAllCheck: false,
});

Understanding Results

Confidence Scores

| Scenario | Valid | Confidence | Meaning | | ------------------------ | ------- | ---------- | ----------------------------- | | Invalid format | false | 0% | Email syntax is invalid | | No DNS records | false | 0% | Domain cannot receive email | | SMTP rejected (5xx) | false | 0% | Mailbox doesn't exist | | SMTP timeout/error | true | 50% | Could be valid, can't confirm | | Accepted + catch-all | true | 60% | Domain accepts any email | | Accepted + NOT catch-all | true | 95% | High confidence valid |

SMTP Status Values

• accepted - Server returned 2xx to RCPT TO
• rejected - Server returned 5xx to RCPT TO
• unknown - Server returned 4xx or connection failed
• skipped - SMTP check was not performed

Supported Mail Providers

The library automatically detects these mail providers from MX records:

• Google Workspace
• Microsoft 365
• Proofpoint / Proofpoint Essentials
• Mimecast
• Yahoo Mail
• Zoho Mail
• Fastmail
• Proton Mail
• iCloud Mail
• Amazon SES
• SendGrid
• Mailgun
• Postmark
• And more...

How It Works

Verification Pipeline

1. Format Check - Validates email against RFC 5322 pattern
2. DNS Check - Queries MX records, falls back to A record per RFC 5321
3. SMTP Probe - Connects to mail server and tests with RCPT TO
4. Catch-all Detection - Tests with fake x9x0{localpart}@domain

Rate Limiting

The library includes built-in rate limiting to avoid overwhelming mail servers:

• Token bucket algorithm (10 requests per host, 1/second refill)
• Exponential backoff on failures (5s initial, 5min max)
• Automatic recovery after successful requests

Development

# Install dependencies
npm install

# Run tests
npm test

# Run tests with coverage
npm run test:coverage

# Build
npm run build

# Type check
npm run lint

License

MIT