DNSBL Blocklist Directory: Check, Delisting, and Verdicts

Last updated: July 2026

In short: DNS-based blocklists (DNSBLs) protect receiving mail servers globally against spam and phishing, but they vary wildly in authority and reliability. This directory explains the four most commonly encountered blocklists and shows how to check and clear your IP address for free.

When receiving mail servers evaluate incoming SMTP connections, they frequently query real-time DNS databases (DNS-based Blackhole Lists or DNSBLs). If the sending IP address matches a record inside an active blocklist zone, the receiving MTA terminates the session during the initial handshake with a 5xx rejection code.

However, not all blocklists carry equal weight: while industry standards like Spamhaus are trusted directly by Tier-1 email providers worldwide, other operators enforce controversial subscription-based removal fees or have shut down operations entirely.

Major DNSBL Directory and Delisting Guides

Select the specific blocklist referenced inside your bounce messages or reputation monitoring alerts to access detailed breakdowns, honest reputational verdicts, and step-by-step delisting instructions:

1. Spamhaus (SBL & PBL)

Spamhaus is the most authoritative and widely deployed DNSBL in the global email ecosystem. A listing on the Spamhaus Block List (SBL) or Policy Blocklist (PBL) causes immediate hard bounces across Gmail, Microsoft 365, and major tier-1 networks. Delisting is always 100% free once security vulnerabilities are patched:

• Spamhaus Blocklists (SBL & PBL): Check, Delisting, and Verdict

2. SpamCop (SCBL)

The SpamCop Blocking List (SCBL) is an automated, real-time database driven by user complaints and seeded spam traps. Its most powerful feature is automated expiration: once offending spam broadcasts cease, listed IP addresses drop off the database automatically within exactly 24 hours:

• SpamCop Blocking List (SCBL): Check, 24-Hour Delisting, and Verdict

3. UCEPROTECT (Level 1, 2 & 3)

UCEPROTECT separates listings across three tiers. While Level 1 targets single IPs for direct abuse, Level 2 and Level 3 penalize entire subnets and Autonomous Systems. Because of its controversial paid whitelisting model (whitelisted.org), Level 2 and Level 3 listings are ignored by major email providers:

• UCEPROTECT Level 1, 2 & 3 Blocklist: Check, Fees, and Verdict

4. SORBS (Discontinued in 2024)

The Spam and Open Relay Blocking System (SORBS) shut down permanently in 2024. Its DNS zones no longer answer queries. If your Postfix or Exchange server still checks inbound IPs against SORBS today, it causes unnecessary connection timeouts and delays:

• SORBS Blocklist Shutdown: Why dnsbl.sorbs.net Was Discontinued in 2024

Core Rules for Blocklist Delisting

• Never pay for removal: Legitimate blocklists such as Spamhaus and SpamCop never charge delisting fees. Any third-party expedited removal offer or paid “whitelisting subscription” (such as UCEPROTECT Level 2/3) is either a scam or completely ignored by major receiving networks.
• Resolve the root cause first: Before submitting any removal application, ensure your outbound mail queues are cleared, compromised web scripts are patched, and subscriber lists enforce double opt-in verification.

Verifying your configuration

To confirm that your email server infrastructure is fully secured, properly authenticated with SPF, DKIM, and DMARC, and free of DNS misconfigurations, audit your domain instantly using the free MXAudit scanner.