IP Blacklist Checker

Why check if your IP is blacklisted?

A blacklisted IP address means your emails will be rejected or marked as spam by major providers (Gmail, Outlook, Yahoo). IP blacklists, also known as DNSBLs (DNS-based Blackhole Lists) or RBLs (Realtime Blackhole Lists), are queried by receiving mail servers before they accept an email. This check looks at your mail server IP address, not a phone IMEI, an iPhone block, or a device ban.

Impact of a blacklisted IP:

• Rejected emails (bounce) with "550 blocked" or similar messages
• Emails in spam even with correct SPF, DKIM and DMARC
• Damaged reputation that can linger even after delisting

Three reasons to check regularly:

• Detect a problem before your customers report it
• Identify a compromised server sending spam without your knowledge
• Verify a new IP before using it in production

What is a DNS blacklist (DNSBL)?

A DNS blacklist, also called a DNSBL, RBL or Blackhole list, is a published list of IP addresses with a poor sending reputation. Receiving mail servers query these lists in real time, over DNS, before they accept a connection. If your sending IP is found on a list the receiver trusts, your message can be rejected outright or routed straight to spam.

Spamhaus is the most widely used provider: its ZEN zone combines the SBL (confirmed spam sources), the XBL (compromised hosts and botnets) and the PBL (policy listing for dynamic ranges) in a single lookup. Barracuda and SpamCop are the other two lists that the major mailbox providers lean on.

How does the blacklist check work?

When you send an email, the receiving server can check your IP against a blacklist with a reverse DNS query. The octets of the IPv4 address are reversed and prepended to the list's zone:

# To check the public IP 192.0.2.1 on Spamhaus ZEN:
dig A 1.2.0.192.zen.spamhaus.org

# Response if listed (return codes 127.0.0.x):
127.0.0.2  -> SBL (confirmed spam source)
127.0.0.4  -> XBL (compromised IP / botnet)
127.0.0.10 -> PBL (dynamic / residential policy)

# Response if clean:
NXDOMAIN (no record = not listed)

This tool runs that lookup across a curated set of authoritative lists at once, interprets the 127.0.0.x return codes, and turns them into a single clear verdict instead of a raw pile of zone answers.

Understanding your verdict and reputation score

The result leads with a 3-tier verdict, and the score supports it:

• Clean : no listing on any authoritative list.
• At risk : a borderline or informational signal, or a single low-weight listing worth watching.
• Listed : found on at least one authoritative list, deliverability is impacted now.

The verdict is backed by a 0 to 100 reputation score and a grade, weighted by each list's authority rather than a flat "listed on N of M" count:

Authoritative lists vs informational lists

Not every listing is an alarm, and this is the key thing most tools get wrong:

• Authoritative lists move the verdict and the score: Spamhaus ZEN (SBL, XBL), Barracuda BRBL, SpamCop SCBL, Invaluement and PSBL. A listing here hurts deliverability at Gmail, Outlook and Yahoo.
• Informational lists are shown for context but do not affect deliverability at the major mailbox providers: Spamhaus PBL, UCEProtect L2 and L3, and dynamic or PTR-policy lists. They are never displayed as a "blacklisted" alarm.

Blacklists checked by the tool

Authoritative lists (used by Gmail, Outlook, Yahoo)

Informational lists (no impact on major-provider deliverability)

These informational lists are never shown as a blacklist alarm: the major mailbox providers do not use them to reject mail.

Why does an IP get blacklisted?

The most frequent causes of a listing:

• Sent spam, intentionally or because the server was compromised
• Open relay or a misconfigured MTA that anyone can send through
• Dynamic IP sending direct to MX, instead of relaying through the ISP
• Inherited reputation from the previous owner of a recycled IP
• Snowshoe spamming, where volume is spread thin across many IPs to dodge thresholds

Keep in mind that a Spamhaus PBL entry is a policy listing, not evidence of abuse: it simply says the range should not be sending mail direct to MX.

Email sender and server IP reputation

A DNSBL listing is only one part of your sender reputation. Mailbox providers also weigh broader, often owner-authenticated signals that a public lookup cannot read:

• Cisco Talos and Sender Score publish a reputation grade for a sending IP.
• Google Postmaster Tools exposes your IP and domain reputation as seen by Gmail.
• Microsoft SNDS reports the data Outlook sees, once you authenticate as the IP owner.

This tool tells you whether you are listed on authoritative DNSBLs. For the full picture, enroll your sending IP in Postmaster Tools and SNDS and watch those dashboards over time. There is no live third-party reputation data shown here, only deep-link guidance.

How to delist your IP (per provider)

Fix the root cause before you request removal. Spamhaus and most lists relist fast if the spam, open relay or compromise is still active, so clean up first: rotate credentials, close the relay, patch the server, stop the offending mail flow.

Spamhaus

SBL listings are resolved through the IP owner or your ISP. CSS and XBL listings are self-service and auto-expire once the issue stops. PBL listings can be removed with a self-service exclusion if you run a legitimate static-IP mail server. Start at the Spamhaus lookup and removal page.

Microsoft and Outlook

Outlook does not use a public DNSBL the same way: use the Microsoft deliverability support / sender remediation form to request mitigation, and enroll in SNDS so you can see and act on the data Outlook collects for your IP.

Barracuda BRBL

Barracuda has no auto-expiry. Submit the Barracuda removal request form; removals are typically processed within around 12 hours once the cause is fixed.

SpamCop

SpamCop is 100% automatic. Once the reports stop, the listing expires on its own, usually within 24 to 48 hours. There is no form to file, just stop the offending mail.

For a step-by-step walkthrough, see the IP blacklist removal guide.

Public IP vs private IP

Only public, routable IP addresses can appear on a DNSBL. Private RFC 1918 ranges, used inside local networks, are never globally reachable, so they cannot be listed:

• 10.0.0.0/8 (10.x.x.x)
• 172.16.0.0/12 (172.16.x.x to 172.31.x.x)
• 192.168.0.0/16 (192.168.x.x)
• 127.0.0.1 (localhost)

If you are unsure, check the public IP your mail server actually sends from, which is the source IP receiving servers see, not the private LAN address of the machine.

IPv6 blacklist coverage

DNSBL coverage for IPv6 is intentionally thin. The address space is too large to enumerate, and per-/128 listings would blow up resolver caches and create QNAME-minimization fan-out, so most lists publish IPv6 data sparingly. This tool is honest about it:

• IPv4-only lists are skipped on a v6 input, never silently counted as "clean".
• A v6 listing is almost always a block or range listing (a /64 or wider), not the exact /128 address you entered.

When in doubt for an IPv6 sender, confirm the result against your provider's own reputation dashboard.

FAQ - Frequently asked questions

Q: How do I know if my mail server IP address is blacklisted?

A: Enter your IP address in the tool above and click 'Check'. In seconds you get a verdict (clean, at risk or listed), a reputation score (0-100) and a grade (A+ to F) computed against a curated set of authoritative lists (Spamhaus ZEN, Barracuda, SpamCop, Invaluement, PSBL).

Q: Why is my IP on a blacklist?

A: Common causes: spam sent (intentionally or via a compromised server), an open relay, a dynamic IP sending direct to MX, or reputation inherited from a previous owner. A Spamhaus PBL entry is a policy listing for dynamic ranges, not an accusation of spam.

Q: What does it mean when my IP is listed?

A: It depends on the list. A listing on an authoritative list (Spamhaus ZEN, Barracuda, SpamCop) hurts deliverability at Gmail and Outlook. A listing on an informational list (PBL, UCEProtect L2/L3) is shown for context but does not block your mail at the major providers.

Q: How do I remove (delist) my IP from a blacklist?

A: Each list has its own procedure, and you must fix the root cause first or you will be relisted. Spamhaus CSS/XBL auto-expire; SpamCop auto-delists 24 to 48h after reports stop; Barracuda needs a manual form (around 12h).

Q: Which blacklists matter most?

A: Spamhaus ZEN, Barracuda BRBL and SpamCop, because Gmail, Outlook and Yahoo use them. UCEProtect L2 and L3 are not used by the major mailbox providers and should not be treated as an alarm.

Q: My IP is on Spamhaus PBL, is that serious?

A: Not necessarily. The PBL lists IPs that should not send mail direct to MX (residential, dynamic). If you run a legitimate mail server on a static IP, request a self-service exclusion via the Spamhaus form.

Q: What is the difference between an IP blacklist and a domain blacklist?

A: A DNSBL (IP) lists the addresses of spamming servers. A URIBL/SURBL (domain) lists domains found in spam content. Test both with the domain blacklist checker for a complete diagnosis.

Q: Can a private IP (192.168.x.x) be blacklisted?

A: No. Only public, routable IPs appear on DNSBLs. Private RFC 1918 ranges (10.x, 172.16 to 172.31.x, 192.168.x) and localhost cannot be listed. Check the public IP your mail server sends from.

Q: How often should I check my sending IP reputation?

A: After every server or IP change. For production servers, weekly or monthly is good hygiene. Check immediately if your emails start bouncing or landing in spam.

Complementary tools

Useful resources

• Spamhaus - lookup and delisting (official procedures)
• Barracuda Central - removal request (BRBL delisting form)
• RFC 5782 - DNS Blacklists and Whitelists (DNSBL technical specification)
• Spamhaus vs Barracuda vs SpamCop (which list matters and why)
• Google - Email sender guidelines (Gmail requirements)