How to check if your mail server is blocklisted

Receivers look up the server that sent each message in blocklists, also called DNSBLs. When it is listed, the mail lands in spam or is refused, even with SPF, DKIM and DMARC in order. A Domain & email monitor asks blocklists about your own mail servers twice a day, together with the email check.

Turn it on

There is nothing extra to set up. Every Domain & email monitor with Check email authentication on is checked. See how to check SPF, DKIM and DMARC to add one.

Which lists

• SpamCop lists servers that people recently reported spam from.
• PSBL lists servers that sent mail to its spam traps.
• UCEPROTECT, level 1, lists single servers that sent mail to its spam traps.

What is checked

We check the addresses of mail servers you run yourself: those your SPF record names with ip4, a and mx, and your MX hosts, up to 16 per domain. Some things are not checked:

• Shared mail services, such as Google Workspace, Microsoft 365 and Mailchimp. They send for thousands of customers, and only they can act on a listing. If all your mail goes through them, the monitor says there is nothing of its own to check.
• Other companies’ servers that your SPF record includes.
• IPv6 addresses, because most blocklists don’t support them. Private addresses and SPF ranges of more than 8 addresses aren’t checked either.

Where to see it

• The monitor’s page has a Blocklists tile: Not listed, On followed by the list’s name, or Nothing to check.
• Below it, the Blocklists section shows which addresses were checked, every listing with the list’s reason and its removal page, and what wasn’t checked.
• If a list doesn’t answer, it shows under Couldn’t check, and we ask again at the next check.

When a server is listed

A listing counts as a problem in the domain’s email grade. The monitor’s alert channels hear about it once, when it first appears, not every day after.

1. Fix the cause first: a hacked website form or account, an infected computer, or a server that relays mail for anyone. Otherwise the server is listed again.
2. Then get it off the list. How depends on the list, see below.
3. The next check, at most 12 hours later, shows whether it is gone.

Getting off each list

• SpamCop removes a server by itself 24 hours after the last report. See SpamCop’s blocklist page.
• PSBL: request removal at psbl.org/remove.
• UCEPROTECT level 1 listings expire 7 days after the last spam it saw. You don’t need to pay for express removal. Look up the address at uceprotect.net.

More on email authentication monitoring.