What an MX record check proves
An MX record is DNS telling the internet which servers accept mail for a domain. No MX record means no mail server, which means every address on that domain is undeliverable — the send fails at the first hop, before any mailbox question arises.
That is why MX checking removes more bad addresses per second than anything else. It is also all it does: it validates the domain, never the individual mailbox.
What a pass means
The domain is configured to receive mail. It says nothing about whether j.smith@ exists, whether the mailbox is full, or whether the server will accept mail from your IP. A domain with MX records can still have thousands of fabricated addresses on it.
What a fail means
Three distinct states matter, and they are not the same:
- NXDOMAIN — the domain does not exist. Every address is dead. Delete.
- No MX record — the domain exists (a website, a parked page) but cannot receive mail. Also dead for email purposes.
- MX present — mail is accepted. Keep, subject to other checks.
A domain with an A record and no MX is the case most naive filters miss: it looks alive because the website loads, and every address you send to bounces.
Where it sits in a real cleaning pipeline
Normalise, dedupe, repair typos, then MX-check. It is cheap, cacheable per domain (a 50,000-row list might have 8,000 unique domains), and it removes the failure class that is guaranteed rather than probable. Mailbox-level verification — an SMTP conversation per address — comes after, and costs money per address.
Why do it in a browser
DNS is public data. A lookup only reveals a domain name, never a person or an address, so the check can run from your browser against a public resolver with nothing uploaded to a vendor. ListSweep queries Google and Cloudflare resolvers directly and caches each domain's answer, so a large list resolves quickly without a queue.
Check your own list in about 30 seconds. Paste or drop a CSV — duplicates, typos, role addresses and dead domains, all handled in your browser. Free for the first 100 addresses, $19 once for unlimited.
Open the toolCommon questions
Is MX checking the same as email verification?
No. Verification usually adds SMTP probing, catch-all detection and disposable/role classification. MX checking is the domain-level subset — the cheapest, fastest and least intrusive part.
Can MX records be wrong?
They can be stale for a few hours after a domain changes providers, and misconfigured domains do exist. Treat a failure as strong evidence rather than absolute proof, and re-check if you have reason to doubt it.
Last updated 2026-10-23.