Catch throwaway emails with one API call

A disposable address service hands out inboxes on its own domains, so the domain tells you more than the local part. Checking it needs no contact with anyone: it is a DNS read and a list match.

Our check never opens a connection to the mail server, so it cannot say whether a particular mailbox exists. The response states this with smtp_checked: false on every result.

The disposable field is true when the domain, or any parent domain, appears on the open disposable-email-domains list. That list is released under CC0 and maintained by contributors who add domains by pull request ¹. Matching parents means a subdomain of a listed domain is flagged too.

The list's own maintainers say they cannot guarantee that every entry is still disposable, only that basic checking was done so each was disposable at some point ¹. Plan for the occasional false positive: send a flagged signup to a softer path rather than a hard block when the cost of a lost customer is high.

The same call reads the domain's public DNS. It reports MX records, the SPF and DMARC policies, whether the domain is a free mailbox provider, and whether the local part is a role name such as info or support. A domain that publishes a null MX record is declaring that it accepts no mail at all ², and the response marks it null_mx and undeliverable.

The function below uses the global fetch built into current Node versions and returns a verdict you can act on. It treats a network failure as an error you handle yourself, rather than silently letting the signup through.

1const API = 'https://YOUR_API_HOST';
2​
3export async function checkSignupEmail(email) {
4  const res = await fetch(API + '/v1/email-domain-check', {
5    method: 'POST',
6    headers: {
7      Authorization: 'Bearer ' + process.env.LOOKVALID_API_KEY,
8      'Content-Type': 'application/json',
9    },
10    body: JSON.stringify({ email }),
11  });
12  const body = await res.json();
13  if (!res.ok) throw new Error(body.error.code + ': ' + body.error.message);
14  if (!body.found) return { allow: false, why: body.reason };
15  const d = body.data;
16  if (d.disposable) return { allow: false, why: 'disposable domain' };
17  if (d.deliverability_signal === 'undeliverable') return { allow: false, why: 'domain accepts no mail' };
18  return { allow: true, review: d.deliverability_signal === 'risky' };
19}
20​
21console.log(await checkSignupEmail('new.user@example.org'));

The last line is a sample call (top-level await needs an ES module). Each found result costs 1 credit, and a domain that does not exist comes back as a free found: false.

• Block on disposable only where a throwaway account does real damage, such as free trials with a cost to you.
• Allow and flag when the signal is risky for another reason, for example a role mailbox.
• Never treat good as proof that a person exists. It means the domain is set up to receive mail.
• Cache your own verdicts for a domain for a few days; the API also serves a repeated lookup from its own cache for free.

For the full response and every reason code, see the email domain check product page, or try a domain in the email domain checker. New to the API? Start with the quickstart.