1. Confirm what actually failed
Keep the recipient address, time of the attempt and full bounce message. Determine whether the problem affects one sender, one mailbox or every mailbox on the domain. A misspelled address, full inbox or spam-folder rule can look like a DNS issue from the outside.
2. Compare MX with your provider’s setup
Look up the domain after the recipient’s @. Check each hostname and preference against the mail provider’s current account instructions. Do not copy a record from an unrelated domain: some providers issue tenant-specific destinations.
If the tool reports Null MX, the domain has published an explicit no-mail policy. If it returns no MX, investigate whether incoming mail was ever configured. NXDOMAIN points you toward the queried name and DNS delegation, rather than a particular mailbox.
3. Check who hosts authoritative DNS
The place you bought the domain is not always the place that currently serves its DNS. Verify the active nameservers in your registrar account before editing records. After a nameserver migration, check that the intended MX records exist at the new DNS provider.
4. Allow for existing caches
Use both resolver options and note the time and remaining TTL in each answer. Different answers after a recent change can reflect independent caches. Lowering TTL after a change cannot shorten the lifetime of a copy that was already cached.
There is no universal countdown for every resolver on the internet. If both answers remain unexpected, check the authoritative configuration rather than repeatedly changing records.
5. Separate DNS errors from missing records
A temporary resolver failure or DNSSEC validation problem can prevent an answer even when a domain has MX records. Retry using the second resolver. If both fail, investigate DNS availability and DNSSEC configuration with your DNS provider. Do not interpret a failure as permission to remove DNSSEC or recreate all records.
6. Continue beyond DNS
When records match the provider’s instructions, check mailbox provisioning, service status, quota, delivery logs and the bounce code. SPF, DKIM and DMARC concern email authentication; MX records alone cannot show whether those policies pass. This tool sends no email and does not open SMTP connections.
A useful support report includes the domain, both resolver results, lookup times, the last DNS change and the original bounce. Remove personal message contents before sharing it publicly.