Is my IP blacklisted? How to check and get delisted

By InboxProof · 7 min read

If your emails suddenly stopped arriving, one of the first things to check is whether your sending IP is on a blocklist. A blocklist (also called a blacklist or RBL, for "real-time block list") is a database of IP addresses known to send spam. Major mailbox providers like Gmail, Outlook, and Yahoo check these lists before accepting your mail. If your IP is listed, your email gets rejected or sent straight to spam.

Quick check: The free IP blocklist checker tests your sending IP against 9 major blocklists including Spamhaus, SpamCop, Barracuda, and UCEPROTECT. No email needed.

What is a blocklist?

A blocklist is a database maintained by anti-spam organizations that lists IP addresses (and sometimes domains) known to send spam. When a mailbox provider receives an email, it checks the sender's IP against these lists. If the IP is listed, the email is rejected or flagged as spam.

The most common blocklists include:

Spamhaus (sbl, pbl, xbl.spamhaus.org): the most widely used blocklist
SpamCop (bl.spamcop.net): a community-driven blocklist
Barracuda (b.barracudacentral.org): used by many enterprise mail servers
CBL (cbl.abuseat.org): a large community blocklist
UCEPROTECT (dnsbl-1, dnsbl-2.uceprotect.net): checks for open relays and spam
SORBS (dnsbl.sorbs.net): a comprehensive blocklist

How to check if your IP is listed

You can check your IP against a blocklist by doing a DNS lookup. The blocklist uses a special DNS format where you reverse the IP octets and append the blocklist domain.

For example, if your IP is 1.2.3.4, you would check:

4.3.2.1.sbl.spamhaus.org for Spamhaus SBL
4.3.2.1.bl.spamcop.net for SpamCop

If the DNS lookup returns an IP address (usually in the 127.0.0.x range), your IP is listed. If it returns "not found," your IP is clean.

Doing this by hand across 9 blocklists is tedious. The InboxProof blocklist checker does it for you in one click, testing your IP against all 9 major lists at once.

Why does it matter?

Blocklist listings are one of the most common causes of sudden deliverability drops. If your IP gets listed, your emails will be rejected by major mailbox providers, and you'll see bounce rates spike. This can happen for several reasons:

Your IP was previously used by a spammer (common with new or recycled IPs)
Your email was reported as spam by recipients
Your IP is shared with other senders who are sending spam
Your server has an open relay or misconfigured SPF/DKIM/DMARC

How to get delisted

If your IP is listed, you need to request delisting. Most blocklists have a delisting process:

Spamhaus: Use their check tool to see why you're listed and request delisting
SpamCop: Use their delisting form
Barracuda: Use their delisting request

Before requesting delisting, make sure you've fixed the underlying issue. If you're still sending spam or have a misconfigured server, you'll get re-listed.

Prevent future listings

The best way to avoid blocklist listings is to maintain good email hygiene:

Use a dedicated IP for your sending domain
Monitor your sender reputation
Keep your bounce rate low
Respond to spam complaints quickly
Warm up new IPs gradually
Set up proper SPF, DKIM, and DMARC records

Check your IP reputation now

Run the free IP blocklist checker and see if your sending IP is on any of the 9 major blocklists.

Check my IP

Want this checked automatically every day? Inboxproof Pro monitors your domain around the clock and alerts you the moment a record breaks or an IP gets listed. See pricing →