Your IP is on a blacklist — now what?

Finding your IP address on a blacklist can be alarming, but it doesn't always mean something is wrong. This guide explains what blacklists are, what the different types mean, and exactly what to do about it.

What is an IP blacklist?

An IP blacklist (also called a DNSBL — DNS-based blackhole list) is a real-time database of IP addresses that have been associated with spam, malware, or other malicious activity. Email servers, firewalls, and security systems query these lists to decide whether to accept or block traffic from a particular IP.

There are dozens of blacklists, each maintained by a different organisation with different criteria. Being listed on one doesn't necessarily mean the same thing as being listed on another.

Types of blacklists — and which ones matter

Not all blacklist listings are equal. Understanding the type of listing tells you whether you need to take action.

When to worry (and when not to)

Don't worry if...

You're only listed on Spamhaus PBL — this is normal for any non-mail-server IP. You're on one or two reputation lists with a low AbuseIPDB score — your IP might have been dynamically assigned to someone who sent spam before you got it. The listing appeared and disappeared within a day or two — many lists auto-expire.

Investigate if...

You're listed on SBL, XBL, or Abuse.ch — these indicate real security problems. Your AbuseIPDB confidence score is above 25% — multiple people have reported your IP. You're listed on three or more separate blacklists simultaneously — this suggests genuine malicious activity. The listing persists for more than a week — something is still actively wrong.

Act immediately if...

You're running a mail server and it's on the SBL — your email is being blocked. You see XBL listings — a device on your network is likely compromised. Your business IP is listed and you're noticing email delivery failures, blocked website access, or client complaints.

How IPs get listed

Understanding why an IP ends up on a blacklist helps you fix the problem and prevent recurrence.

Infected devices — the most common cause for business networks. A laptop, IoT device, or server on your network is infected with malware and is sending spam or participating in a botnet without anyone knowing. This is exactly what network monitoring tools like Ignix are designed to detect.

Compromised email accounts — an employee's email password has been stolen (often via phishing) and their account is being used to send spam. Check your email server logs for unusual sending patterns.

Open relays or misconfigured services — a mail server, proxy, or DNS resolver is misconfigured and being exploited by third parties to send spam or amplify attacks.

Previous IP user — if your ISP uses dynamic IP assignment, you might inherit an IP that was previously used by someone involved in spam. This is common and usually resolves on its own.

Shared hosting — if you're on shared web hosting, another customer on the same server could be responsible for the listing.

How to get delisted — step by step

Delisting by provider

How to prevent future listings

Keep devices updated — unpatched operating systems and firmware are the primary way malware gets onto networks. This includes routers, IoT devices, and printers — not just computers.

Use strong, unique passwords — compromised email accounts are a major source of blacklistings. Use a password manager and enable two-factor authentication.

Monitor your network traffic — most blacklist-worthy activity happens without anyone noticing. A device sending spam at 3am won't show up until the IP is listed and email starts bouncing. Continuous monitoring catches this early.

Configure your mail server properly — if you run your own mail server, ensure SPF, DKIM, and DMARC records are correctly set up. Don't run an open relay.

Check regularly — use ignixip Blacklist Check periodically to catch listings before they cause problems.