Email Security
Open Blacklist Check →Choose the address that sends mail
A website address, inbound mail server and outbound sending server may be different systems. For a delivery incident, identify the actual outbound public IPv4 address from the sending provider or message evidence. Entering a domain in Blacklist Check tests its resolved public IPv4 addresses; it does not automatically discover every outbound mail source. MX records describe inbound routing and may only provide a starting clue.
Understand this tool’s coverage
The configured DNS blocklists support IPv4. The tool rejects private or reserved addresses, URLs and CIDR ranges, and does not provide an IPv6 reputation result. A domain check examines up to 16 unique resolved IPv4 addresses and reports omissions. Review provider-level results, errors and limits. The absence of a listing on the configured sources is narrower than a universal reputation verdict.
Read a listing in context
A listed result needs investigation with the relevant provider’s explanation. Different lists can describe different policies or categories. A failed or unavailable lookup is not a clean answer, and another provider may reach a different conclusion. Keep the IP, provider and time of the result, then compare them with the mail rejection message. Some delivery failures have no relationship to a public blocklist.
Fix the cause before requesting removal
Review the mail server’s sending activity, compromised accounts, relay configuration and provider guidance. If a listing is relevant, follow that provider’s official removal process after addressing the cause. Separately check SPF, DKIM, DMARC and reverse DNS. Correct DNS and an unlisted IP do not guarantee inbox placement; recipients can apply their own reputation and content policies.
Worked example
Illustrative example — not a live test Website A record: 192.0.2.10 Outbound sending IP: 192.0.2.25 Check the sending IP for the delivery incident. These are documentation addresses, not public test targets.
What to check next
- Identify the actual outbound IPv4 address.
- Review each provider’s status, including unavailable checks.
- Investigate sending behavior and use the provider’s official guidance.
Common questions
Does “not listed” guarantee delivery?
No. It describes the checked sources at that time, not every recipient’s filtering decisions.
Can I use this check for IPv6 reputation?
The configured blocklists do not support that here. Do not interpret an unsupported IPv6 check as clean.