When email suddenly starts bouncing or landing in spam, a blacklist is one of the first things to rule out. Mail providers check every incoming message against public lists of addresses and domains known for sending spam, and a single listing can be enough to get your mail refused. The checker above finds the servers that handle a domain’s email, looks up each address on more than a dozen widely used blocklists and checks the domain itself on the main domain lists. When something is listed, it shows which list, what the listing means and where to request removal.

What an Email Blacklist Is

An email blacklist, also called a blocklist or DNSBL, is a public list of IP addresses or domains that have been linked to spam, malware or abuse. They are run by security companies, email providers and volunteer groups. Mail servers query these lists in a fraction of a second as each message arrives, and many reject or filter mail from anything that appears on them.

Lists that track IP addresses look at where mail comes from, meaning the server that connected and handed the message over. Lists that track domains look at what is inside the message, mainly the links. A domain can end up on a domain list even if it never sent a single email, simply because spammers linked to it.

What This Tool Checks

Enter a domain and the tool finds its MX records, the servers that receive its email, and checks up to four of their addresses. Enter an IPv4 address and it checks that address directly, which is the better choice when you want to test the server that sends your mail, since sending and receiving servers are often different. For each address, it reports:

• Whether it appears on each IP blocklist, with the ones that matter most marked as major
• What the listing means, where the list gives a reason code, as Spamhaus does
• The address’s reverse DNS name, and whether that name points back to the same address
• A link to each list’s own lookup and removal page

For a domain, it also checks the domain name on the lists most filters use for links inside messages, such as SURBL.

Which Blacklists Matter Most

Not every list carries the same weight. Spamhaus is used by a very large share of the world’s mail servers, so a listing there causes real delivery problems almost everywhere. Barracuda’s list is built into many company firewalls and spam filters, and SpamCop is widely used by smaller mail servers. These are marked as major in the results. Spamhaus limits who can query its lists, so when it does not answer our server, the result says so and points you to its own free lookup page.

Smaller lists are used by fewer servers, and some are known for listing whole networks to pressure hosting companies. A listing on one of them is worth fixing if you know the cause, but on its own it rarely explains a widespread delivery problem. If your mail is being rejected everywhere, look first at the major lists and at authentication records such as SPF, DKIM and DMARC.

How to Read Your Results

The top of the result gives a one-line verdict. Green means no list flags the domain or its mail servers. Amber means something needs attention but is not a spam listing, such as a policy list entry or a reverse DNS problem. Red means at least one major list has the address or domain listed.

Each list appears as a row with a colored dot. Major lists are always shown, along with any list that flags the address. Lists that came back clear are tucked under a line you can open to see them all. Lists that did not answer are left out of the results, with a note naming them, so a missing list never looks like a clean result.

The Spamhaus Policy List Is Not a Spam Listing

Spamhaus runs several lists, and one of them, the Policy Block List or PBL, works differently from the rest. Internet providers add the address ranges they give to homes and dynamic connections, as a way of saying those addresses should not send email straight to other mail servers. Ordinary computers and phones send mail through their provider or an email service instead, so the PBL catches spam from infected home computers without affecting normal users.

If your own mail server shows up on the PBL, it usually means it sits on a home or dynamic connection. Either move it to a fixed business address and remove it with Spamhaus’s PBL form, or send outgoing email through a relay such as your provider’s mail server or a sending service.

Why Mail Servers Get Listed

Most listings trace back to a handful of causes. An email account with a stolen password is the most common, since spammers use it to send thousands of messages through a legitimate server. Hacked websites are next, often through an old plugin or a contact form that lets anyone send mail. Malware on a computer that shares the same office internet connection can also put the whole address on a list.

Legitimate senders get listed too. Mailing people who never signed up, buying email lists or sending to many old addresses that now bounce can all trigger spam traps, which are addresses that exist only to catch senders with poor list habits.

How to Get Removed From a Blacklist

Removal starts with fixing the cause, because most lists will simply list the address again if spam keeps coming. Change passwords on any account that might be compromised, update or remove vulnerable website software, scan computers on the network and review recent outgoing mail logs for anything unusual.

Once the problem is solved, use each list’s removal page, linked in the results. Spamhaus and Barracuda review requests, usually within a day. SpamCop removes an address on its own about 24 hours after reports stop, and several smaller lists expire listings automatically after a few days without new spam. Paying for faster removal is never required by the reputable lists, and offers to remove you for a fee are best ignored.

Reverse DNS and Email Delivery

Many mail servers check the reverse DNS of the address that connects to them before accepting a message. They expect a proper name, such as mail.example.com, and they expect that name to point back to the same address. Missing reverse DNS, a name that does not match or a generic name assigned by an internet provider can each cause mail to be rejected or scored as spam, even with no blacklist listing.

Reverse DNS is set by whoever controls the address, usually your hosting company, cloud provider or internet provider, rather than in your own domain’s DNS. The results flag any problem with it, and the Reverse DNS Lookup tool explains what to ask your provider for.

Checking Regularly

A listing can appear at any time, and the first sign is often a customer saying they never got your email. If you run your own mail server or send newsletters from your own address, check it every week or two and after any security problem. If your email is handled by a large provider, such as Google Workspace or Microsoft 365, the provider manages its own addresses, and your attention is better spent on SPF, DKIM and DMARC.

Your Checks Stay Private

We do not keep a record of the domains or addresses you check, or anything about who checked them. Each result is held for 15 minutes so a repeated check loads quickly, then deleted. Lookups are made with standard DNS queries from our server, the same way mail servers check these lists.