Start with a repeatable test
Send a short message without attachments from an external account. Check recipient spelling, spam and forwarding. Record time and timezone and preserve complete bounce codes. If storage is full, resolve it without deleting the only copy of important messages.
Check the layer matching the failure
For incoming issues, check MX and mailbox existence. For outgoing issues, review client settings and sender authentication. After a nameserver move, records may have been left at the former provider. Supply support with codes and timestamps, never passwords.
Your practical checklist
- Identify incoming versus outgoing failure.
- Test externally without attachments.
- Preserve codes and timestamps.
- Check the active DNS zone.
A useful question
Should I immediately change nameservers?
No. Diagnose first. A switch without a full zone copy can disrupt more services.
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Sources & further reading
Original guide by chname.ch editorial. Archive dates organise this library; this guide was created and reviewed on . Provider and registry instructions take precedence when requirements change.