DIAGNOSTIC PLAYBOOK
No MX record: why delivery may still be attempted
The absence of MX records does not always mean senders immediately stop delivery attempts. SMTP defines an implicit address-based fallback in applicable cases, unlike the explicit no-service signal of null MX.
HealthCheck Email editorial team · · Examples are illustrative
How to investigate
- Distinguish an empty MX answer from a DNS error or explicit null MX.
- Inspect the domain's address records and whether the intended mail service is actually configured there.
- Publish the provider's MX records for receiving mail, or use an intentional no-service policy when appropriate.
What this looks like
ILLUSTRATIVE EXAMPLE
A web-only domain has an A record and no MX. Some senders attempt SMTP at the web server's address, which does not run a mail service.
A mistake to avoid
Do not rely on missing MX alone to express that a domain must never receive mail. Use an explicit configuration that matches the owner's intent.
Keep the result in context
The authoritative DNS service publishes records; recursive resolvers may retain earlier answers until their cache expires. Save the queried name, record type, resolver, answer and time. A website loading correctly does not establish that email records are present or that an SMTP server accepts mail.
Take the next step
Use the related check to gather evidence, then compare it with the affected message or service. Keep the result and time with your notes so a later change can be distinguished from the original problem.
Sources and further reading
The protocol references below explain the underlying behavior. Your sending or DNS provider supplies the account-specific settings for its service.