Blacklist Troubleshooting

What email blocklists are

Blocklists (often called blacklists) are databases of IP addresses and domains associated with spam or abuse. Receiving servers query them when mail arrives, and a listing can lead to rejection or to mail being filtered as spam. Some lists track IPs, others track domains that appear in message content or links.

Lists differ widely in how they work and how much weight receivers give them. Well-known examples include the Spamhaus lists, Barracuda and SpamCop. Many smaller lists exist too, with varying influence. Part of our job is telling you which listings actually matter to your delivery.

Receivers also keep their own internal reputation systems, which aren’t public lists at all. A clean blocklist check doesn’t guarantee good placement, so we look at both.

Signs you may be listed

• Bounces that name a blocklist or include a link to a lookup page.
• A sudden rise in rejections from business mail servers.
• A monitoring tool or checker showing your IP or domain listed.
• Your hosting provider forwarding an abuse report.
• A new server whose IP was previously used by someone else.

Common causes of a listing

• Mailing addresses that were never opted in, including purchased or scraped lists.
• Old lists containing spam traps: addresses that no longer belong to real people or were never used to sign up.
• A compromised account, website form or server sending spam without your knowledge.
• An open relay or weak password on your mail server.
• A shared IP where another sender caused the problem.
• Inherited reputation from the IP’s previous owner.

How we work

1. Identify: check your IPs and domains against the major lists and confirm which ones receivers are actually citing.
2. Investigate: review logs, recent campaigns, list sources, sign-up forms and server security to find what triggered the listing.
3. Fix the cause: close a relay, secure a compromised account, remove a bad list segment, add confirmation to a sign-up form, or whatever the evidence points to.
4. Request removal: follow each list’s own delisting process, providing accurate information about what was fixed.
5. Verify: confirm removal and watch for re-listing.
6. Explain: give you a plain account of what happened and how to avoid it.

What’s included

• A listing check across relevant IP and domain blocklists.
• A root-cause investigation with evidence.
• Security fixes where the cause was a compromise or misconfiguration.
• List and sign-up recommendations where the cause was list quality.
• Delisting requests filed through each list’s official process.
• Ongoing blocklist monitoring if you want it.

If a compromise was involved, we also help you rotate passwords and review access so the same route can’t be used again.

Why we fix first and delist second

Many lists remove entries automatically after a period, or on request, but will list you again quickly if the behaviour continues. Repeated listings can make future removal slower. Delisting without fixing the cause usually brings the problem back within a week or two.

What affects timeline and cost

• Number of IPs, domains and lists involved.
• How clear the cause is from the available logs.
• Whether security remediation is needed.
• Each list’s own removal process and timing, which we don’t control.

Common mistakes

Requesting removal repeatedly without changing anything. Paying for delisting services that promise quick removal without investigation. Panicking over a minor list that receivers rarely use while missing a major one. Moving to a new IP and carrying the same list with you.

Related: email deliverability optimization, email monitoring and maintenance, all email infrastructure services, the guide, and contact.

Frequently asked questions