Email Blacklists (DNSBL/RBL) - Complete Guide

There are thousands of blocklists managed by various organizations, each with different specifications for how a domain or IP ends up on their list. Sometimes known as a DNSBL (Domain Name System Blacklist) or RBL (Realtime Blackhole List), these services are spam blocking lists used by ISPs and mailbox providers to filter unwanted email.

Some lists have a more significant impact on email delivery than others. Below we have compiled a comprehensive list of the most commonly encountered blocklists, organized by their impact level.

High Impact Blocklists

Organizations listed as high-impact have the greatest effect on email delivery and can cause significant bounce rates.

Major IP Blacklists

Major Domain/URI Blacklists

Medium Impact Blocklists

Organizations listed as medium-impact have the potential to impact email delivery but are less widely used than high-impact lists.

Specialty IP Blacklists

Policy and Relay Blacklists

Regional and Community Blacklists

Low Impact Blocklists

Organizations listed as low-impact are unlikely to significantly impact email delivery but may be used by some smaller providers.

Malware and Exploit Blacklists

Miscellaneous Operator Blacklists

Understanding Blacklist Impact

High Impact Blocklists

These are the most critical lists that can cause significant delivery problems: - Spamhaus is the most well-respected and widely used blocklist in the world. A listing at Spamhaus will have a negative effect on your ability to deliver emails and can cause bounce rates of over 50%. Evidence suggests that most of the top North American ISPs use Spamhaus to inform blocking decisions. - Barracuda is widely used by enterprise email security appliances and can significantly impact B2B email delivery. - SpamCop can have a significant impact on B2B email campaigns, though it is not as widely used by major North American ISPs.

Medium Impact Blocklists

These lists can impact delivery but are less widely used: - SORBS uses several methods to identify potential spammers. Most of their lists use spam traps to identify problematic senders. SORBS will also list a sender based on user complaints or if administrators have received spam from the sender. - UCEPROTECT maintains multiple levels of blacklists, with Level 1 being the most commonly used. - Abusix provides commercial blacklist services that are used by many European ISPs and enterprises.

Low Impact Blocklists

These lists are unlikely to significantly impact delivery but may be used by smaller providers: - Many of these are regional or specialized lists that focus on specific types of abuse or geographic areas. - Some are community-maintained lists that may not have the same level of accuracy as major commercial lists.

How to Check Your Status

You can check if your IP address or domain is listed on any of these blacklists using our Spam Database Lookup Tool. This tool will check your IP or domain against all the major blacklists listed above and provide detailed information about any listings found.

Getting Delisted

If you find yourself listed on a blacklist, the process for removal varies by list:

1. Identify the listing reason - Most blacklists provide information about why an IP or domain was listed
2. Fix the underlying issue - Address the root cause (spam, open relay, malware, etc.)
3. Contact the blacklist operator - Follow their specific delisting procedures
4. Wait for removal - Delisting can take anywhere from a few hours to several days

For more information about getting off email blacklists, see our guide: How to Get Off of Email Blacklists