DIAGNOSTIC PLAYBOOK
Equal-priority MX servers receive different messages
MX servers with equal preferences may both receive traffic. A broken peer can therefore cause intermittent delivery even when another server at the same priority works well.
HealthCheck Email editorial team · · Examples are illustrative
How to investigate
- Enumerate every target at the shared preference and test resolution and SMTP readiness individually.
- Confirm that all peers recognize the same recipient domains and addresses.
- Correlate failing deliveries with the contacted target and repair the inconsistent peer.
What this looks like
ILLUSTRATIVE EXAMPLE
Two MX servers have preference 10. One accepts the new mailbox and the other rejects it because recipient synchronization failed.
A mistake to avoid
Changing preference values can conceal the inconsistency without fixing it. A backup or peer may still receive mail during other failures.
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.