Validate email addresses in JavaScript

1. Let the browser do the first check

<input type="email" name="email" required autocomplete="email">

type="email" gives mobile users the right keyboard and blocks obviously broken input before the form is sent. Check input.validity.valid or listen for the invalid event to show your own message.

2. A practical format check

const EMAIL = /^[^\s@]+@[^\s@]+\.[^\s@]{2,}$/;

function looksLikeEmail(value) {
  const email = value.trim();
  return email.length <= 254 && EMAIL.test(email);
}

looksLikeEmail("anna@example.com"); // true
looksLikeEmail("anna@example");     // false

Don’t write a strict home-made regex. Such patterns often reject real customers (o'brien@example.ie, anna+news@example.com) and still accept asdf@asdf.com. Our email syntax checker shows the individual rules if you need them.

3. Catch typos

Most invalid sign-ups are typos in popular domains: gmial.com, hotmial.com, yaho.com. Suggest a correction instead of rejecting:

const DOMAINS = ["gmail.com", "yahoo.com", "hotmail.com", "outlook.com", "icloud.com"];

function suggest(email) {
  const [user, domain] = email.toLowerCase().split("@");
  const close = DOMAINS.find((d) => d !== domain && levenshtein(d, domain) <= 2);
  return close ? `${user}@${close}` : null;
}

(Any small Levenshtein function works; the email validation API also returns a did_you_mean suggestion.)

4. Check that the mailbox exists (Node.js)

Only a check against the recipient’s mail server tells you whether anna@example.com really exists. Do it on your server:

// Node.js 18+ (built-in fetch)
async function validateEmail(email) {
  const url = `https://api.emailvalidation.io/v1/info?email=${encodeURIComponent(email)}`;
  const res = await fetch(url, { headers: { apikey: process.env.EMAILVALIDATION_KEY } });
  if (!res.ok) throw new Error(`Validation failed: ${res.status}`);
  return res.json();
}

const result = await validateEmail("anna@example.com");
if (result.state === "undeliverable") {
  // reject: the address does not exist
} else if (result.disposable) {
  // ask for a permanent address
}

The response contains state (deliverable, undeliverable or unknown), a reason, a score and the flags format_valid, mx_found, smtp_check, catch_all, disposable, role and free.

Recommended flow for sign-up forms

1. type="email" plus the regex for instant feedback.
2. Typo suggestion when the field loses focus.
3. API check on submit (server side). Block undeliverable and disposable, accept the rest.
4. If the API is slow or down, accept the address: never block sign-ups because of a validation outage.

Try it without code in the email validator.