@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

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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.

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Installation

npm install @stackverify/email-check

yarn add @stackverify/email-check

pnpm add @stackverify/email-check

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Quick Start

Full Validation (Node.js)

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

const result = await checkEmail("user@gmail.com");

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("user@example.com");

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

CommonJS

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

checkEmail("user@example.com").then((result) => {
  if (!result.isValid) {
    console.log(`Invalid: ${result.reason}`);
  }
});

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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").

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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.

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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

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Bulk Validation

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

const emails = [
  "real.user@gmail.com",
  "throwaway@tempmail.com",
  " typo@broken-domain ",
  "nobody@doesnotexist12345.xyz",
];

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}`);
  }
}

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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").

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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.

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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.

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Contributing

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

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License

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

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Author

Morgan Miller · StackVerify

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