How to Check If a Domain Is on an Email Blacklist

If your email open rates dropped suddenly, your bounce rate spiked, or a client is reporting that their campaigns stopped working a blacklist listing is one of the first things to check. It's fast to verify and it's one of the most common causes of sudden deliverability problems.

This guide covers how to check, which blacklists actually matter, what a listing means for deliverability, and what to do about it.

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What is an email blacklist

An email blacklist (also called a DNS-based Blackhole List or DNSBL) is a database of IP addresses and domains that have been flagged for sending spam or exhibiting suspicious sending behavior. Mail servers check these lists in real time when processing inbound email and use the results to decide whether to deliver, spam-folder, or reject the message.

There are hundreds of blacklists. Most of them don't matter. A small number are checked by enough mail servers that a listing has real deliverability impact.

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Which blacklists actually matter

Spamhaus is the most important. The Spamhaus Block List (SBL), Exploits Block List (XBL), and Policy Block List (PBL) are checked by the majority of enterprise mail servers worldwide and by major mailbox providers. A Spamhaus SBL listing can effectively stop email delivery to a large portion of the internet.

Barracuda is widely used by business email security systems. A Barracuda listing disproportionately affects B2B email if your clients are sending to businesses, Barracuda matters.

SpamCop is used by a significant number of mail servers. Listings here are often temporary and expire quickly, but during the listing window deliverability is impacted.

SORBS (Spam and Open Relay Blocking System) is checked by many mail servers, particularly in Europe and Asia-Pacific.

URIBL and SURBL check URLs in email bodies against domain blacklists. If a domain used in links inside your email is listed, the email may be flagged even if the sending domain is clean.

Microsoft SNDS (Smart Network Data Services) is specific to Outlook and Hotmail delivery. If your clients send to significant numbers of Microsoft email users, this matters.

Google Postmaster Tools isn't technically a blacklist but functions like one for Gmail delivery. Google maintains its own domain reputation system that affects inbox placement at Gmail.

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How to check blacklist status

Manual check

The fastest manual check is MxToolbox's blacklist checker at mxtoolbox.com/blacklists.aspx. Enter a domain or IP address and it checks against around 100 blacklists simultaneously and shows which ones have a listing.

For each check:

1. Run the domain name (example.com)
2. Run the sending IP address (get this from your ESP's sending logs or email headers)

Both matter. A clean domain on a blacklisted IP still has deliverability problems.

Reading email headers

To find the sending IP for a specific campaign:

1. Pull a raw email from the campaign (in Gmail: three-dot menu → "Show original")
2. Look for the Received: headers the first one shows the originating IP
3. Run that IP through the blacklist checker

Checking multiple blacklists directly

For Spamhaus specifically, check directly at check.spamhaus.org. Their tool gives more detailed information about why a listing occurred than third-party checkers.

For Barracuda, check at barracudacentral.org/lookups.

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What a listing actually means

Not all listings have equal impact. The severity depends on which blacklist and how widely it's used.

Spamhaus SBL listing Serious. Major impact across most mail servers. Requires immediate action.

Barracuda listing Significant for B2B sending. Less impact for B2C depending on recipient mix.

SpamCop listing Moderate impact, often temporary. Usually expires within 24–48 hours if sending stops.

SORBS listing Variable impact. Some servers check SORBS strictly, others don't check it at all.

Minor or obscure blacklists Often minimal real-world impact. Some third-party checkers flag listings on blacklists that almost no mail server checks. Don't panic about every listing.

The key question for any listing: how many of your recipients use mail servers that check this blacklist? A listing on a blacklist that no relevant mail server checks has zero deliverability impact.

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What to do if you find a listing

Step 1: Don't ignore it

Even if the deliverability impact seems minor right now, listings can escalate. A minor listing combined with continued high complaint rates can trigger additional listings on more serious blacklists.

Step 2: Identify the root cause

Before requesting delisting, understand why you were listed. Submitting a delisting request without fixing the underlying issue usually results in re-listing within days.

Common causes:

• Spam trap hits sending to old, invalid, or never-valid email addresses
• High complaint rates recipients marking email as spam
• Sudden volume spike sending significantly more email than usual without warming up
• Compromised account someone sent spam from your domain or IP without your knowledge
• Shared IP contamination another sender on your shared ESP IP triggered the listing

Step 3: Submit a delisting request

Most major blacklists have a delisting process:

Spamhaus check.spamhaus.org provides a delisting form. They typically require you to explain the root cause and what you've changed. Response time is usually 24–48 hours.

Barracuda barracudacentral.org/lookups click "Request removal" after entering the IP. Barracuda's automated system processes most requests quickly if there's no active spam pattern.

SpamCop SpamCop listings typically expire on their own within 24–48 hours if sending stops. Manual delisting is available but often not necessary.

SORBS sorbs.net has a delisting process but can be slow. Often worth waiting for automatic expiry.

Step 4: Fix the root cause

Whatever caused the listing needs to be addressed before resuming full send volume:

• List hygiene: remove invalid addresses, spam trap addresses, and disengaged contacts
• Confirm opt-in: ensure new subscribers went through a verified opt-in process
• Reduce send frequency: if complaint rates were high, give your list time to reset
• If shared IP: work with your ESP to move to a different IP pool or dedicated IP

Step 5: Monitor after delisting

Delisting doesn't fully restore reputation immediately. In the days after a delisting, send to your highest-engagement segments first and monitor bounce and complaint rates closely. Full reputation recovery typically takes 1–2 weeks of clean sending.

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How often to check blacklist status

For agencies managing client domains, a one-time manual check isn't sufficient. Blacklist status changes continuously a domain can be listed and delisted multiple times in a month, and each listing happens without warning.

The right cadence for agencies is continuous automated monitoring checking blacklist status hourly for every domain in your portfolio. When a listing appears, you get an alert immediately rather than finding out when campaign numbers come in.

This is the difference between catching a blacklisting at hour one and catching it after three campaigns have sent to degraded deliverability.

At the individual domain level, checking monthly or before major campaign sends is better than not checking at all. But for agencies managing client email infrastructure, manual periodic checks aren't sufficient too much can change between checks.

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Quick reference

| Blacklist | Matters for | Check at | Delisting | |---|---|---|---| | Spamhaus SBL | Everyone | check.spamhaus.org | Manual request, 24–48h | | Barracuda | B2B email | barracudacentral.org | Automated, fast | | SpamCop | General | mxtoolbox.com | Auto-expires 24–48h | | SORBS | General | sorbs.net | Manual or auto-expire | | URIBL/SURBL | URLs in email body | uribl.com / surbl.org | Contact directly | | Microsoft SNDS | Outlook/Hotmail | sendersupport.olc.protection.outlook.com | Portal request |