Inputs
Example
example.com -> MX preference, exchanger host, first A and AAAA answers, and Null MX or CNAME warnings.
MX Record Check
Query MX records through DNS-over-HTTPS, sort priorities, resolve first hosts, and spot Null MX or CNAME problems.
Good for mail-routing sanity checks before touching DNS, mail gateways, or provider configuration.
What MX records decide — and what they don't
MX records are the routing table of email: they name the hosts willing to receive mail for a domain and the order in which senders should try them. Almost every delivery mystery starts here, because MX is where DNS intent and mail reality first touch — a domain can have perfect SPF and DMARC and still lose mail to a stale exchanger, a CNAME target that violates the standard, or a forgotten Null MX that politely tells the world the domain accepts nothing.
This check reads the published MX set, sorts it by preference, resolves the first exchangers to A and AAAA addresses, and calls out the routing patterns that cause real incidents: missing records, Null MX, CNAME targets, and dead hostnames. It is deliberately a DNS-only view — no SMTP connection is opened — which makes it fast, safe, and honest about which layer it examines.
From lookup to routing diagnosis
Enter the domain and read the interpretation before the raw records: the ordering, the preference values, and the warnings often answer the actual question directly. Lower preference wins; equal preferences distribute across hosts. Then check whether the first exchangers resolve — both IPv4 and IPv6 — because a hostname without addresses, or one that only resolves in one address family, produces exactly the kind of intermittent delivery failure that is miserable to debug from the outside.
For delivery incidents, pair this result with evidence from the other direction: the Received chain of a real message shows which exchanger actually accepted the mail, and the domain's SPF, DKIM, and DMARC records govern whether it was trusted after arrival. Routing and authentication fail differently — MX problems tend to lose or delay mail wholesale, authentication problems file it in spam — and knowing which family you are in halves the search space.
Resolution paths without SMTP contact
The domain is sent only after you start the lookup; the browser tries Cloudflare DNS-over-HTTPS first and falls back to the same-origin DNS helper if that path fails. The tool does not open SMTP sessions, does not test STARTTLS, and cannot prove delivery from any particular sender — it shows what DNS currently instructs senders to do, which is a necessary truth but not the whole one. The page keeps no lookup history, though resolvers and hosting infrastructure keep their own operational logs.
Frequently asked questions
What does a lower MX preference mean?
Lower values are tried first; senders only move to higher-preference hosts when the preferred ones fail. Equal values let the sender pick freely, which is how simple load distribution across exchangers is done.
What is Null MX and when is it right?
A single MX record with preference 0 and a target of just a dot declares that the domain accepts no mail at all. For genuinely mail-free domains it is the correct, explicit signal — much better than leaving senders to time out against nonexistent servers.
Why is a CNAME as MX target flagged?
Because the standards require MX targets to be hostnames with address records, not aliases. Many receivers tolerate CNAME chains, but tolerant is not the same as reliable — some sending implementations mishandle them, producing failures that only certain peers ever see.
Why does the tool show A and AAAA records?
To confirm the advertised exchangers actually exist as addresses, and in which address families. A host that resolves only over IPv4 while a sender prefers IPv6 is a classic source of asymmetric delivery behavior.
A backup MX looks dead — is that urgent?
Sooner rather than later, yes. In quiet times nobody notices, but senders fall back to higher-preference hosts exactly when the primary struggles — the moment a dead backup turns a partial outage into lost mail.
Are queried domains stored by this app?
The page does not save a lookup history. The DNS provider and normal hosting infrastructure may still keep their own operational logs, like any network service.