Validates MX records for proper email routing
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Domain — takes the hostname of the audited URL and strips one leading www., so https://www.example.com/contact is audited as example.com. An empty or malformed URL, or one without a hostname, ends the audit with 501.
Lookup — queries the MX records of that domain through the system resolvers, with no cache. A resolver failure (SERVFAIL, timeout) ends the audit with 500: it is not a missing record. NXDOMAIN and NODATA count as "no MX records".
Rules — no MX record at all fails (400); a domain whose MX records all point at the root (0 ., the RFC 7505 null MX) warns (300).
Aggregate — FAIL wins over WARNING; when at least one MX record points at a real host the audit is SUCCESS (200) and the message lists the hosts sorted by preference.
Specification pin — every run emits 37A-DnsMailMxAuditor-100 (INFORMATION), naming RFC 5321 Simple Mail Transfer Protocol §5.1 (October 2008). It does not change the overall status.
Every row maps to one checkRule* method and one CheckCode, in the order the auditor runs them. CheckCode suffixes use status ranges: 100 information, 200 success, 300–399 warning, 400–499 fail, 500–599 error.
| CheckCode | Status | When it fires | Recommendation | Why it matters |
|---|---|---|---|---|
37A-DnsMailMxAuditor-100 | INFORMATION | Always. Records the specification this auditor implements. | — (recommendation is null; nothing for the site to change) | — |
37A-DnsMailMxAuditor-400 | FAIL | The domain publishes no MX record at all (NXDOMAIN, NODATA or an empty answer). | Publish at least one MX record for {domain} pointing at the server that accepts its email, for example "{domain}. MX 10 mail.{domain}.". | Without MX records, sending servers fall back to the domain's web address, so email from customers and partners bounces or is lost unless the web server also runs mail. |
37A-DnsMailMxAuditor-300 | WARNING | Every MX record of the domain is the RFC 7505 null MX (0 .), which declares that the domain accepts no email. | If {domain} should receive email, replace the null MX record "{records}" with MX records pointing at its mail servers; if it is meant to never receive email, no change is needed. | A null MX tells every sending server to reject mail for the domain on the spot, so a domain that is expected to receive email loses every message addressed to it. |
37A-DnsMailMxAuditor-200 | SUCCESS | At least one MX record points at a real host. Message lists the hosts sorted by preference: "{domain} publishes {count} MX records: {host} (priority {priority}), …". | — | — |
37A-DnsMailMxAuditor-500 | ERROR | The resolver could not answer the MX query (SERVFAIL, timeout, network error). | Make sure the name servers of {domain} answer MX queries, then run the audit again. Last error: {error}. | — |
37A-DnsMailMxAuditor-501 | ERROR | The audited URL is empty, malformed or has no hostname to query. | Provide a URL with a scheme and a hostname, for example https://example.com/; received "{url}". | — |
| Status | Description | Test logic |
|---|---|---|
| SUCCESS | The domain publishes MX records | At least one MX record points at a real host (200); the check data lists domain, mxRecords (priority, target, sorted by preference), mxCount and mxHosts. |
| WARNING | The domain declares it accepts no email | Every MX record is the null MX 0 . (300). |
| FAIL | The domain has no MX records | The MX query answered NXDOMAIN, NODATA or no records (400). |
| ERROR | The auditor could not run the check | Resolver failure (500); empty, malformed or host-less URL (501). |
| INFORMATION | Specification pin | Always emitted (100); does not change overall status. |
Contact forms, order confirmations, password resets and replies from customers all depend on senders finding the domain's mail server. A domain without MX records receives whatever the fallback to its address record happens to deliver, which is usually nothing.
A null MX (0 .) is a deliberate, valid statement that the domain never receives email (RFC 7505). It is right for a domain used only for a website or for sending, and wrong for one that has mailboxes, so this auditor warns rather than fails.
The domain is the hostname of the audited URL minus one leading www.. A page on shop.example.com is audited as shop.example.com, whose MX records may legitimately differ from example.com.
The auditor queries DNS only. It does not connect to the listed mail servers, check that they resolve, or test SPF, DKIM or DMARC (see the other DNS Mail auditors).
A domain that mixes a null MX with real hosts violates RFC 7505; the auditor reports the real hosts as a success and leaves the null MX in the check data.
A null MX (0 .) used to be reported as SUCCESS with an empty host; it is now a WARNING (300).
An empty, malformed or host-less URL used to be a FAIL; it is now an ERROR (501), because nothing about the domain was observed.
A resolver failure (SERVFAIL, timeout) used to be reported as "no MX records" (FAIL); it is now an ERROR (500), so a transient DNS problem no longer looks like a missing record.
Unexpected exceptions used to be caught and returned as FAIL; the core now reports them as ERROR.
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