What is an MX record?
An MX (Mail Exchange) record is a DNS entry that specifies which mail server is responsible for receiving email for a domain. Without a valid MX record, a domain cannot accept email, so checking MX is a fast first step in verifying an address.
What MX records do
When a sender wants to deliver mail to user@example.com, it queries DNS for example.com's MX records to learn which server handles incoming mail. The MX record points to a hostname (like mail.example.com), and a domain can list several with priority values so mail can fail over to a backup server.
MX records are what make email routing work across the internet. They're configured by whoever manages the domain's DNS, and they change when a company switches email providers — for example from self-hosted mail to Google Workspace or Microsoft 365.
Why MX matters for verification
If a domain has no MX record (and no fallback A record set up for mail), it simply cannot receive email — every address at that domain is undeliverable. Checking MX is therefore a cheap, fast filter that rules out entire dead domains before any slower SMTP probing.
A valid MX record doesn't prove a specific mailbox exists, but its absence proves the address can't work. Mailbeam returns an mx_check boolean in every response and uses it as an early gate in the verification pipeline.
MX checks in practice
An MX lookup is a DNS query, so it's fast and puts no load on the recipient's mail server. It's ideal for pre-filtering large lists: drop the addresses on domains with no mail infrastructure, then run the more expensive checks only on the survivors.
It also helps diagnose delivery problems — if your mail to a domain is failing, a missing or misconfigured MX record is a common culprit.
In practice
Verifying contact@deadstartup.io, Mailbeam queries DNS and finds no MX record — the domain was abandoned and no longer receives mail. It returns mx: false and marks the address undeliverable immediately, without wasting an SMTP probe.
Frequently asked questions
Verify emails with confidence
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