@stackverify/email-check

High-performance email validation library for Node.js and the browser.

Validate syntax, detect disposable emails, verify DNS/MX records, and score inbox delivery likelihood — zero dependencies, fully tree-shakeable.

Installation · Quick Start · API · Tree-Shaking · Contributing

Why email-check?

Validating email addresses goes far beyond regex. @stackverify/email-check gives you a fast, lightweight, multi-layer validation pipeline that catches invalid syntax, blocks disposable throwaway addresses, verifies the domain can actually receive mail, and estimates whether the message will land in the inbox or the spam folder.

| Capability | What it does | Browser | Node.js | |---|---|---|---| | Syntax validation | Regex-based RFC-light syntax check | ✅ | ✅ | | Disposable detection | Flags 5,100+ known throwaway domains | ✅ | ✅ | | Domain existence | DNS A/AAAA record lookup | ❌ | ✅ | | MX record check | Verifies the domain can receive email | ❌ | ✅ | | Inbox scoring | Rates delivery likelihood (low / medium / high) | ✅ | ✅ |

• Zero dependencies — nothing to install, nothing to audit.
• Dual-format — ships ESM and CommonJS out of the box.
• Fully typed — first-class TypeScript declarations.
• Tree-shakeable — import only what you need via sub-path exports.
• 312 KB dist total — the disposable domain database compresses to ~27 KB gzipped.

Installation

npm install @stackverify/email-check

yarn add @stackverify/email-check

pnpm add @stackverify/email-check

Quick Start

Full Validation (Node.js)

import { checkEmail } from "@stackverify/email-check";

const result = await checkEmail("[email protected]");

if (!result.isValid) {
  console.error(`Rejected: ${result.reason}`);
} else {
  console.log(`Accepted — inbox score: ${result.inbox.score} (${result.inbox.label})`);
}

Browser-Only (Syntax + Disposable)

import { checkEmail } from "@stackverify/email-check";

// In the browser, DNS checks are skipped automatically.
const result = await checkEmail("[email protected]");

console.log(result.syntax);     // true
console.log(result.disposable); // false

CommonJS

const { checkEmail } = require("@stackverify/email-check");

checkEmail("[email protected]").then((result) => {
  if (!result.isValid) {
    console.log(`Invalid: ${result.reason}`);
  }
});

API Reference

checkEmail(email: string): Promise<EmailCheckResult>

Runs the full validation pipeline. Returns a result object.

Result Object

| Property | Type | Description | |---|---|---| | isValid | boolean | true if the email passed every applicable check. | | syntax | boolean | true if the email matches a valid syntax pattern. | | disposable | boolean | true if the domain is a known disposable / throwaway provider. | | domainExists | boolean | true if the domain resolves via DNS. false in browsers. | | hasMX | boolean | true if the domain has MX records. false in browsers. | | inbox | { score: number; label: "low" \| "medium" \| "high" } | Delivery likelihood estimate. | | reason | string \| null | Human-readable reason the email was rejected, or null if valid. |

Possible reason values

| reason | Meaning | |---|---| | "Invalid email syntax" | The address does not match a valid email format. | | "Disposable email provider" | The domain is a known temporary / throwaway service. | | "Domain does not exist" | DNS lookup failed — the domain is not registered. | | "Domain cannot receive email" | The domain has no MX records. | | null | The email passed all checks. |

Sub-Path Imports

Import only the pieces you need — bundlers will tree-shake the rest.

// Just syntax validation (111 bytes gzipped)
import { isValidSyntax } from "@stackverify/email-check/syntax";

// Just disposable detection (281 bytes gzipped + data)
import { isDisposable } from "@stackverify/email-check/disposable";

// Just inbox scoring (241 bytes gzipped)
import { inboxScore } from "@stackverify/email-check/inbox-score";

isValidSyntax(email: string): boolean

Synchronous syntax check. Returns true if the email matches /^[^\s@]+@[^\s@]+\.[^\s@]{2,}$/.

isDisposable(domain: string): boolean

Synchronous check against a database of 5,100+ known disposable email domains. Supports subdomain matching (e.g. sub.mailinator.com is flagged).

inboxScore(domain: string): { score: number; label: "low" | "medium" | "high" }

Returns a delivery likelihood score. Trusted providers (Gmail, Outlook, Yahoo, iCloud, Proton, Zoho) receive a score of 95 ("high"). All other valid domains receive 70 ("medium").

Tree-Shaking & Bundle Size

The library is designed for minimal bundle impact. If you only need one capability, import the sub-path directly:

// Your bundler (webpack, Vite, esbuild, Rollup) will only include what you import.
import { isValidSyntax } from "@stackverify/email-check/syntax";

| Import | Raw | Gzipped | |---|---|---| | @stackverify/email-check (full) | 1.5 KB | 527 B | | @stackverify/email-check/syntax | 97 B | 111 B | | @stackverify/email-check/disposable | 584 B | 281 B | | @stackverify/email-check/inbox-score | 402 B | 241 B | | Disposable domain data | 70 KB | 27 KB |

The disposable domain database is the primary payload. If you do not need disposable detection, avoid importing it and your total cost is under 1 KB gzipped.

Validation Pipeline

checkEmail() runs checks in order and returns early on the first failure:

Email input
  │
  ▼
 Syntax check ──────── fail → "Invalid email syntax"
  │
  ▼
 Domain extraction ─── fail → "Invalid email domain"
  │
  ▼
 Disposable check ──── fail → "Disposable email provider"
  │
  ▼
 Domain exists ─────── fail → "Domain does not exist"    (Node.js only)
  │
  ▼
 MX record check ───── fail → "Domain cannot receive email"  (Node.js only)
  │
  ▼
 Inbox scoring
  │
  ▼
 isValid = true

Bulk Validation

import { checkEmail } from "@stackverify/email-check";

const emails = [
  "[email protected]",
  "[email protected]",
  " typo@broken-domain ",
  "[email protected]",
];

for (const email of emails) {
  const result = await checkEmail(email);

  if (!result.isValid) {
    console.log(`SKIP  ${email} — ${result.reason}`);
  } else if (result.inbox.label === "low") {
    console.log(`WARN  ${email} — low inbox score`);
  } else {
    console.log(`OK    ${email} — score ${result.inbox.score}`);
  }
}

Trusted Providers

The following email providers are classified as high trust (inbox score 95):

| Provider | Domain(s) | |---|---| | Gmail | gmail.com, googlemail.com | | Microsoft | outlook.com, hotmail.com | | Yahoo | yahoo.com | | Apple | icloud.com | | Proton | proton.me, protonmail.com | | Zoho | zoho.com | | StackVerify | stackverify.site |

All other valid domains receive a score of 70 ("medium").

Node.js vs Browser

| Feature | Node.js | Browser | |---|---|---| | Syntax validation | ✅ | ✅ | | Disposable detection | ✅ | ✅ | | Domain existence (DNS) | ✅ | ❌ Skipped | | MX record check | ✅ | ❌ Skipped | | Inbox scoring | ✅ | ✅ |

The library auto-detects the runtime. DNS-based checks are only performed in Node.js — in the browser they are silently skipped, so domainExists and hasMX remain false.

Use Cases

• SaaS signup forms — block disposable emails at registration.
• Marketing platforms — verify list quality before sending campaigns.
• Fraud prevention — flag suspicious or temporary email addresses.
• Lead generation — score and prioritize contacts by email quality.
• Authentication flows — validate emails during signup or password reset.

Contributing

Contributions are welcome! Please see CONTRIBUTING.md for guidelines.

License

MIT — free for personal, commercial, and SaaS use.

Author

Morgan Miller · StackVerify

Built and maintained by the StackVerify team as part of our marketing and SaaS toolkit.