Mail Blacklist Checker
Check your IP or domain against major email blocklists instantly
Frequently Asked Questions
Related Tools
What is an Email Blacklist?
An email blacklist (also called a DNSBL or RBL) is a real-time database of IP addresses and domains that have been identified as sources of spam, malware, or other abusive email. When your mail server sends a message, the receiving server checks the sender's IP against one or more of these lists before deciding whether to accept, reject, or flag the message.
Blacklists use the DNS protocol for fast lookups. The receiving mail server reverses the sender's IP address and queries it as a subdomain of the blacklist's zone. For example, to check 138.252.126.33 against Spamhaus ZEN, the server queries 33.126.252.138.zen.spamhaus.org. If a DNS record is returned, the IP is listed. The response code indicates the type of listing.
Common blacklist response codes (Spamhaus)
127.0.0.2 → SBL (Spamhaus Block List) — known spam source
127.0.0.3 → SBL CSS — spam from botnets
127.0.0.4 → XBL (Exploits Block List) — compromised host
127.0.0.10 → PBL (Policy Block List) — dynamic/residential IP
NXDOMAIN → Not listed (clean)
Being listed on even one major blacklist can devastate email deliverability. Messages may bounce with 5xx errors, be silently dropped, or land in spam folders. For businesses, this means invoices go unseen, support replies never arrive, and marketing campaigns fail. At NetOz, we monitor our mail server IPs (like 138.252.126.33 for smtp.netoz.au) against all major blacklists to ensure clean delivery for our customers.
Spamhaus and Major Blacklist Providers
Spamhaus is the most influential email blacklist provider, used by the majority of email providers worldwide including Google, Microsoft, and Yahoo. Their listings carry significant weight — a Spamhaus listing can block your email to billions of inboxes. Understanding the major providers helps you prioritise which listings to address first.
Spamhaus ZEN
A combined zone that includes the SBL (known spam sources), XBL (exploited hosts like open relays and compromised machines), and PBL (dynamic and residential IPs that shouldn't send mail directly). ZEN is the single most widely queried blacklist. PBL listings are policy-based, not punitive — they indicate IPs that should route mail through a proper mail server rather than sending directly.
Spamhaus DBL
A domain-based blacklist that checks the domain names used in email (envelope sender, From header, URLs in the body). Unlike IP-based lists, DBL catches spam from senders who rotate through many IPs but reuse the same domains.
SpamCop (BL)
A crowd-sourced blacklist where users report spam. Listings are automatic and typically expire within 24–48 hours once reports stop. SpamCop is fast to list but also fast to delist, making it a good early warning indicator of spam complaints.
Barracuda (BRBL)
Maintained by Barracuda Networks based on their email security appliance data. Widely used by organisations running Barracuda spam filters. Delisting requires submitting a removal request and demonstrating the spam issue is resolved.
SORBS
The Spam and Open Relay Blocking System lists IPs involved in spam, open relays, open proxies, and dynamic address ranges. SORBS also maintains a DUHL (Dynamic User and Host List) for residential and dynamic IPs.
This tool checks your IP against all of these providers and more in a single query, so you can quickly identify which lists are causing your delivery problems.
How to Remove Your IP from a Blacklist
Getting delisted requires two steps: fix the underlying problem that caused the listing, then request removal from the blacklist provider. Skipping the first step will result in immediate re-listing.
Identify the Root Cause
Check your mail server logs for unusual outbound volume. Common causes include compromised email accounts (weak passwords), hacked web applications sending spam (vulnerable contact forms or CMS plugins), open relays that allow unauthenticated sending, malware on a machine behind your IP, or a legitimate mailing list with poor list hygiene hitting spam traps.
Stop the Spam
Reset compromised account passwords and enable two-factor authentication. Patch or remove vulnerable web applications. Close open relays by requiring SMTP authentication. Scan for and remove malware. If the issue is list hygiene, remove bouncing addresses and implement double opt-in.
Request Delisting
Each provider has its own delisting process. Spamhaus offers a self-service removal tool at their website — SBL listings require explaining what you've done to fix the issue. SpamCop listings expire automatically within 24–48 hours once reports stop. Barracuda has an online removal request form. SORBS requires creating an account and submitting a delisting request.
Prevent Future Listings
Set up proper email authentication with SPF, DKIM, and DMARC records. Monitor outbound mail volume for anomalies. Use rate limiting on SMTP to cap the damage from a compromised account. Regularly check your IPs with this tool. At NetOz, we run automated blacklist monitoring for all customer mail servers hosted in our Adelaide data centre.
Shared IP Considerations
If you're on shared hosting and another user on the same IP is sending spam, your email can be affected too. In these cases, contact your hosting provider (or contact NetOz) to report the issue. Dedicated IP addresses for email sending give you full control over your reputation, which is why NetOz provides dedicated mail IPs for business hosting customers.
Validate your email authentication with the SPF Validator, check mail server DNS with MX Lookup, or analyse email headers with the Email Header Analyzer.