Email Blacklist Check

Email Blacklist Check

Enter an email address or a domain in Email address or domain and click Check. You can paste it however you have it:

• [email protected]
• example.com
• Jane Doe <[email protected]>, copied from a mail client
• mailto:[email protected], copied from a link
• an IP address, to check one server directly

The tool finds every mail server for the domain and every address of each server. It checks:

• the domain against 15 domain blocklists
• each IPv4 address against 42 IP blocklists, starting with the most widely used
• each IPv6 address against the 11 of those lists that accept IPv6 lookups

Stop cancels a check that’s still running, and Clear starts over.

Example: gmail.com

The report opens with a summary: gmail.com isn’t on any of the 15 domain blocklists, and none of its 10 mail-server addresses is listed.

Those 10 addresses belong to five servers:

The priority sets the order: servers sending mail to Gmail try the lowest number first and fall back to the alt servers if it can’t be reached. Mail can arrive through any of them, so each address gets its own row. Each IPv4 address is listed on 0 of 42 lists, and each IPv6 address on 0 of 11.

One list, DrMX, answered for the first address but returned a DNS error for the other four. Those four rows show Could not check, with the reason, rather than counting as listings. Small lists go down now and then, so if a row says that, run the check again later.

Two kinds of blocklist

Domain blocklists such as Spamhaus DBL, SURBL and URIBL list domains that appear in spam, usually as links in the message. If your domain is on one, mail that mentions your domain can be filtered, whichever server sends it. That includes a newsletter or invoice service sending on your behalf.

IP blocklists such as Spamhaus ZEN, SpamCop and Barracuda list the addresses that spam is sent from. Receiving servers look up the sending IP while the message is arriving, and some refuse the connection outright if it’s listed.

IPv6 addresses

Only 11 of the 42 IP lists accept IPv6 lookups, so that’s how many each IPv6 address is checked against. They include the most widely used ones: Spamhaus ZEN, SpamCop and Barracuda. Many smaller lists only ever collected IPv4 data.

That matters because a lot of mail now travels over IPv6. When both servers support it, Gmail, Outlook and most large providers deliver over IPv6. A server that’s clean on IPv4 but listed on IPv6 can still have mail refused, and an IPv4-only check would miss it.

Check the server that sends your mail, too

There’s one limit to keep in mind. A domain’s MX records name the servers that receive its mail, and those are the ones the tool finds and checks. On a small setup the same machine often receives and sends, so a listed MX usually means a listed sender. But mail you send often leaves from somewhere else:

• Google Workspace and Microsoft 365 send from large shared pools.
• Contact forms and shop notifications usually go out from your web server.
• Newsletters go out through the sending service’s own IPs.

To check the IP your mail actually leaves from, open a message you sent and look at the Received: lines in its headers. The lowest one added by your provider shows the sending IP. Enter that IP here.

While you’re at it, check its reverse DNS with IP to Hostname. Many receiving servers reject mail from an IP whose hostname doesn’t match.

Reading a listing

Each listing is explained in plain words, with the raw code the list returned and a look up / delist link to that list’s own page. For example:

PBL: a dynamic or end-user address that should not send mail directly

That one comes from Spamhaus’s Policy Block List, and it isn’t a penalty. It covers home and mobile connections, which aren’t supposed to deliver mail directly. If your server shows up there, either it’s running on that kind of connection and should send through your provider’s mail server, or the owner of a static range can request removal.

Listed and Could not check are kept apart on purpose. A list can fail to answer: it might be slow, return a DNS error, or refuse queries. Spamhaus, for instance, refuses lookups made through big public DNS resolvers. A checker that counted those failures as listings would raise false alarms.

Lists that block whole networks

Some lists don’t judge your server on its own behaviour. UCEPROTECT runs three levels:

A listing on level 2 or 3 means the neighbourhood, not your server. The report says so, and shows these listings apart from listings of the server itself. You can’t clear them by fixing your own server, because they clear when the network improves.

Big mailbox providers rely mostly on their own filtering, so a level 2 or 3 listing on its own is rarely the reason mail bounces. If a bounce message names one, talk to your hosting provider. ASN Lookup shows which network your IP belongs to.

Getting delisted

1. Find the cause first. The usual causes are a hacked email account, a contact form abused by bots, malware on the server, or a newsletter sent to an old list. If you request removal before fixing it, you’ll be listed again within days.
2. Use the look up / delist link in the listing’s row. Each list has its own process. Many remove listings automatically once the spam stops, while others need a request.
3. Run the check again afterwards. Lists update constantly, so a result from yesterday may already be out of date.

Domains that need special handling

• Null MX. Some domains publish MX 0 ., which announces that they never accept email. The report says so instead of pretending to check a server.
• No MX record. Under the email standard (RFC 5321), mail for such a domain goes to the domain’s own address, so that address is checked as its mail server, both IPv4 and IPv6.
• IPv6-only mail servers are checked against the 11 lists that accept IPv6 lookups, and the report makes clear that’s a smaller set.
• Internationalised domains like münchen.de are converted to the form DNS uses (xn--mnchen-3ya.de) before checking.

FAQ

Does a clean result mean my email will arrive?

Not on its own. Gmail and Outlook mostly use their own reputation systems rather than public lists, and they also check SPF, DKIM and DMARC. A clean result rules out one common cause of problems. For delivery to Gmail and Outlook specifically, Google Postmaster Tools and Microsoft SNDS show how those two see your mail.

Why is my server listed when I’ve never sent spam?

Look at which list it is. A network-wide listing (UCEPROTECT level 2 or 3) or the PBL says nothing about your own sending. A spam listing on an individual IP usually means something on the server is sending without your knowledge, such as a hacked password or a vulnerable form.

Why are IPv6 addresses checked against fewer lists?

Most blocklists only collect IPv4 data and don’t answer IPv6 lookups at all. The tool checks IPv6 addresses against every list that does, including the major ones.

Does the check send an email?

No. The tool only looks up DNS records and blocklists. The mailbox isn’t contacted, and only the domain part of the address is used.

How do I see a domain’s mail servers on their own?

Use MX Lookup. To check a single address against blocklists, use IP Blacklist Check.