MX Lookup — Check Mail Server Records Online

What an MX lookup answers

An MX lookup asks DNS which mail servers a domain publishes. It answers one narrow question — can this domain receive mail at all — and says nothing about whether a specific mailbox exists. That makes it a cheap pre-filter: domains with no MX records can be quarantined before you spend verification budget or reputation on them.

This tool queries the exact address domain first, because mail subdomains can publish their own records. Only when DNS is inconclusive does it consult the registrable parent, and unreachable DNS is reported as unknown rather than guessed.

Reading the statuses

Accepts-mail means MX records were published. No-mx means the lookup completed and found none — the domain cannot receive mail as queried. Unknown means DNS could not be reached or refused to answer; treat it as 'try again later', not as a verdict.

• accepts-mail → keep; still validate the address itself
• no-mx → quarantine or drop the domain slice
• unknown → retry later; never delete on unknown

Where MX fits in the validation pipeline

MX checks sit between static validation and any server-side verification, and the order matters. Clean first so formatting noise doesn't pollute the domain set, validate second so disposable and role signals are already flagged, then MX-check the surviving domains: a syntactically valid address on a domain with no mail servers is a guaranteed hard bounce you can remove before it costs reputation. Run the counter afterward so stakeholders see total, unique and deliverable side by side instead of a single inflated headline.

For consumer-heavy lists the MX pass changes little — Gmail, Outlook and Yahoo always publish records — so scope it to the long tail. For B2B lists with hundreds of corporate domains it is the highest-value step in the pipeline: one dead domain often accounts for dozens of addresses, and quarantining the domain slice beats grading each mailbox individually.

• Cleaner → Validator → MX Lookup → Counter is the standard order
• B2B long-tail domains gain the most; consumer mega-providers gain almost nothing
• Quarantine per domain slice, not per address, when no-mx hits

Exact-domain queries and the parent fallback

Mail infrastructure does not always live where you expect. A company can publish MX records on mail.example.com while example.com itself carries none, or route transactional mail through a subdomain with dedicated records. Querying only the registrable parent would misread both cases, so this tool asks the exact domain first and consults the parent solely when the exact query is inconclusive — never as a shortcut.

That conservative fallback is why unknown exists as a first-class status. Corporate resolvers, captive portals and rate-limited DNS all produce non-answers that naive tools report as 'no records.' Here a non-answer stays unknown, the row survives, and the retry happens later on a direct connection rather than as a deletion decision made on bad data.

Privacy model

The lookup runs only when you click, sends domain names only over DNS-over-HTTPS, and never transmits addresses, pasted text or file contents. Up to 100 unique domains per run keep the check fast and abuse-resistant.

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