MediumInfrastructure · usually medium
An MX record points at an alias
MX targets must be hostnames with address records, not CNAMEs.
Check your own domain
What causes this
RFC 2181 states that the target of an MX record must not be an alias. Many mail servers follow the CNAME anyway and delivery works, but some refuse, and the behaviour is not guaranteed. It is the kind of fault that produces intermittent delivery failures from a minority of senders, which makes it unusually hard to diagnose.
What it breaks
Some sending servers may fail to deliver mail to your domain, inconsistently and without an obvious cause.
How to fix it
Point the MX record at a hostname that has A or AAAA records directly.
- Find the hostname the CNAME ultimately resolves to.
- Change the MX record to name that hostname instead, or ask your provider for the correct direct target.
Specification: RFC 2181 §10.3 — MX records must not point to aliases
Related problems
- No email configuration of any kind was foundNo MX, SPF or DMARC records exist for this domain.
- MTA-STS is not configuredThe domain does not publish an MTA-STS policy. This is optional but worth having.
- MTA-STS record published but the policy file is unreachableThe DNS record announces a policy that cannot be fetched.
- An MX host does not resolve to an addressA mail exchanger is published but its hostname has no A or AAAA record.
- No MX records foundThis domain publishes no mail exchangers, so it cannot receive email.