Is my domain blacklisted? How to check your IP reputation

By InboxProof · 6 min read

If your emails suddenly stopped arriving, a blocklist listing is one of the first things to check. A blocklist (or blacklist) is a list of IPs or domains that are known to send spam. Major mailbox providers like Gmail, Outlook, and Yahoo check these lists before deciding whether to accept your email. If your sending IP is listed, your mail will be rejected or sent straight to spam.

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

What is a blocklist?

A blocklist is a database maintained by anti-spam organizations that lists IP addresses and 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.

The most common blocklists include:

Spamhaus (zen.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

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.zen.spamhaus.org for Spamhaus
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.

The InboxProof audit does this automatically for you, checking your sending IP against three major blocklists.

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
Your email was reported as spam by recipients
Your IP is shared with other senders who are sending spam

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, 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

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 →