Start with the provider row
The public checker shows Listed when a provider reports a hit, Not listed when that provider completes a lookup without finding a listing, and Unknown when it cannot provide a usable answer. The report summary describes Unknown rows as unreachable. A completed negative answer is the only one of these states that means Clear for that provider.
Results are limited to the target, providers, and time shown. Providers maintain their own data and may respond differently; no checker result establishes where a receiving mailbox will place a message.
Saved check history may label unresolved rows Failed or Unavailable. The public checker presents an unresolved provider as Unknown (and counts it as unreachable); neither Failed nor Unavailable means Clear.
Listed
The provider returned a hit for the domain or IP you checked.
Confirm the listed target and provider, then compare the result with the affected message’s SMTP rejection details. Review that provider’s listing information, fix the underlying sending or security issue, and follow its own removal process if removal is appropriate.
Clear
The provider lookup completed and reported no listing for this target at that time.
Record the target, provider, and check time. A clear result applies only to that completed lookup; continue checking other provider rows and investigate authentication, policy, reputation, or mailbox causes when delivery is still failing.
Failed
The attempted provider lookup did not complete, so it produced no verdict.
Check that you entered the affected sending domain or the relevant outbound IPv4 address, save the failure time, and retry after a short interval. If it repeats, compare the provider’s own lookup or status information and keep the failed row open in your incident notes.
Unavailable
No usable result from that provider is available for this report.
Treat the provider as unchecked. Retry later or consult the provider directly, and base decisions only on rows with a completed Listed or Clear result.
Keep the evidence in context
Save the checked domain or outbound IPv4 address, provider name, outcome, and timestamp with the relevant delivery error. If a row is Unknown, Failed, or Unavailable, leave it unresolved until a lookup completes or the provider confirms the result. Do not count an unresolved provider as Clear when summarizing exposure.
For background on how blocklists work, read the email blocklist guide. For the broader reputation picture, see the email reputation guide. If a provider confirms a listing, the blocklist removal guide covers provider-specific next steps.
Open the per-provider blocklist checker →