MX record checks: the cheap email validation step everyone skips

Regex-validating an email address only tells you the syntax is plausible. It says nothing about whether [e-mail] can receive mail. An MX record lookup closes that gap for basically zero extra latency.

import { resolveMx } from "node:dns/promises";

async function domainCanReceiveMail(domain) {
  try {
    const records = await resolveMx(domain);
    return records.length > 0;
  } catch {
    return false;
  }
}

This won't catch every typo (an MX record existing doesn't mean the specific mailbox exists — that needs an actual SMTP handshake, which is slow, unreliable, and often blocked by mail servers as spam-probing behavior). But it's a strong, cheap signal that catches a meaningful chunk of junk signups before you send a verification email into the void.

I run this as an optional flag on the email endpoint of Validate — syntax check always runs, MX check is opt-in since it adds a DNS round-trip. Sibling APIs on the same account: QR API and Currency API.