How do I check if my mail server is on a blocklist?

Find the IP address your mail is sent from, then look it up on the lookup pages of the main blocklist operators, such as Spamhaus. Also read any bounce message, which often names the list and gives a link. A listing applies to an IP address or domain, so check the sender your mail really uses.

Why it matters

A blocklist, also called a blacklist or DNSBL (DNS-based blocklist), is a list of IP addresses or domains that mail servers have reason to distrust. Many receivers consult one or more lists while deciding whether to accept mail, so a listing can cause bounces or silent filtering. Knowing which list, and why, tells you what to fix.

How to check

Work out your sending IP. For a mail server you run, it is the server's public address. For website forms, it is whatever host sends the mail. Received headers in a test message show it.
If you send through an email service, the IP may be shared with other customers. Ask the provider whether their pool is listed and who handles delisting.
Read your bounce messages. Phrases such as "blocked using" or "listed at" usually name the list and a URL for more information.
Look the IP up on the operators' own lookup pages. Each list explains its own criteria and delisting process on its site, which is the right place to confirm a listing. Multi-list lookup sites speed up a first pass, but the operator's page is the source of truth.
Also look up your sending domain, since some lists record domains and web addresses as well as IPs.
If you are listed, find and fix the cause first. Typical causes are a compromised account or website form sending spam, an open relay, or an unauthenticated bulk mailing. Then follow the operator's removal process. The steps are in Email blocklist delisting.

Crawvix's scan checks "Not listed on email blocklists" for your domain.

Common mistakes

Requesting removal before fixing the cause, which usually leads to a repeat listing.
Checking the IP of your office or website server when mail is actually sent by a different provider.
Relying on a single lookup tool. Lists differ in what they track and how strictly.
Forgetting that some lists limit or refuse queries from large public DNS resolvers, so a lookup can fail even when you are not listed.

Frequently asked questions

Does being listed mean I did something wrong?

Not necessarily. On shared hosting or a shared mail pool, another customer's behaviour can affect an IP you use. Still, check your own mail for abuse first.

How long does delisting take?

It depends on the list. Some remove entries on request, and others expire entries after a period of good behaviour. Read the operator's policy.

Can authentication stop me being listed?

SPF, DKIM and DMARC do not prevent a listing, but they make it harder for others to send in your name and give you reports that reveal abuse. See Why do my website emails go to spam?.

Want a check of your domain's email health? Try the free website sample.