mx.implicit
No MX Record (Implicit MX)
What we check
We query DNS for MX records at the domain. When none exist, we check for A/AAAA records. RFC 5321 §5.1 specifies that a domain without MX records but with an address record is treated as having an implicit MX pointing to the domain itself at priority 0.
What this finding means
The domain has no MX records, but it does have an A or AAAA record. Sending servers will fall back to delivering mail directly to the IP address of the domain name itself. Mail delivery works, but it relies on the implicit MX fallback rather than an explicit MX configuration.
Why it matters
- Fragile delivery path. The implicit MX mechanism is a compatibility fallback, not a recommended configuration. Not all sending implementations handle it identically.
- No redundancy possible. Without MX records, there is no way to specify backup mail servers with different priorities.
- Ambiguous intent. It is unclear whether the domain is meant to receive email or if MX records were simply forgotten. A domain that genuinely does not accept email should publish a Null MX (RFC 7505) instead.
- No independent mail routing. The mail server must run on the same IP as the domain's web server (or whatever the A record points to), which limits architectural flexibility.
How to fix
Add explicit MX records for the domain:
example.com. IN MX 10 mail.example.com.If the domain does not accept email, publish a Null MX:
example.com. IN MX 0 .
How it's graded
An implicit MX is an informational finding with no grading penalty. It signals a non-standard configuration but does not prevent mail delivery. See Grading Methodology for the full scoring model.
Evidence example
$ dig +short MX example.com
(empty)
$ dig +short A example.com
93.184.215.14
No MX records — implicit MX fallback to the domain's A record