A reference catalog of 47 DNS-based blocklists (DNSBLs) used by mail servers worldwide. Each entry covers what the list targets, how it affects SMTP delivery, and how to request removal when listed. If you’re not sure whether a blocklist is even the cause of your placement problem, start with our 12 most common reasons emails land in spam guide. Click any card to open the full identity page.
Composite zone combining SBL, XBL, and PBL. The most widely deployed IP blocklist in the world. A listing triggers SMTP 550 rejection at MTA level on most mail servers.
User-report-driven listing of IPs that sent spam to SpamCop trap addresses. Widely integrated into spam filters and ESPs. Listings expire automatically in 24-48h.
IP reputation list fed by 200,000+ Barracuda spam sensors. Used natively by Barracuda email security appliances and optionally by any MTA via DNSBL query.
Multi-component blocklist covering IPs involved in spam, malware, and exploit activity. Separate zones for spam, exploits, and domain abuse.
Three-level blocklist: individual IPs (L1), ASN ranges with high spam ratios (L2), and entire ASN blocks (L3). Known for aggressive listing policies.
Passive Spam Block List. Lists IPs that send to its trap network. Removal is automatic once spam stops. Low noise, no human intervention needed.
Lists IPs operating as botnet drones, open proxies, and compromised hosts. Origins in IRC network abuse, also used in mail filter configurations.
Brazilian-origin blocklist combining SPF-based sender validation with traditional DNSBL listing. Primary deployment in Brazil and Latin America.
Right-hand side domain blocklist targeting sending domains and URLs in spam. Checked against From: header domain and message body links by spam scoring engines.
Domain-level list from SORBS. Acquired by Proofpoint in 2011. Maintenance has been inconsistent since. Some legacy filters still query it.
Assigns IPs a reputation score (0-100) rather than a binary listing. Used by major ESPs and mailbox providers as a deliverability weighting factor.
Karma-based IP reputation system. Positive karma for good senders (whitelist), negative for spam sources (blacklist). Yellow zone for unknown senders.
Highest-severity tier of GBUdb’s IP reputation system. Lists IPs with near-zero probability of legitimate mail. Used by SpamStopsHere and enterprise filters.
Reputation-based DNSBL combining spam trap data and complaint signals. Also operates a whitelist (wl.mailspike.net) for senders with verified good sending practices.
Scandinavian-origin DNSBL focused on spam sources. Used as a scoring component in Nordic mail infrastructure and SpamAssassin-based setups.
Family covering dynamic IPs (Dyna), confirmed spam sources (Spam), and IPs with no PTR record (NoPtr). Used in SpamAssassin and Postfix configurations.
Fed by fail2ban reports from participating servers. Covers brute-force attacks, SSH scans, and email abuse in addition to spam. Real-time automated listing.
Lists IPs generating backscatter: misdirected bounce notifications (NDRs) sent to forged sender addresses. Operated by the UCEPROTECT team.
Unsubscribe Blocklist: lists IPs that send mail to addresses that previously unsubscribed. Targets non-compliance with unsubscribe requests, not spam content.
Independent DNSBL with both RBL (IP-based) and standard spam lists. Populated from trap networks and community reports.
Swiss academic network blocklist from SWITCH covering spam sources and worm-infected hosts. Used within Swiss and European academic mail infrastructure.
Japanese DNSBL covering spam sources affecting Japanese mail systems. Primarily deployed in Japanese ISPs and corporate mail environments.
Latin American blocklist targeting spam affecting Spanish-language email users. Primarily deployed in Spain, Mexico, Brazil, and Latin America.
Finnish blocklist covering spam sources identified via local trap networks. Primarily used by Finnish ISPs and regional mail infrastructure.
German DNSBL focused on anonymous mail relay abuse and spam sources affecting German email users and infrastructure.
South African DNSBL family covering IP (ivmsip), 24-hour recent spam (ivmsip24), and URI (ivmuri) zones. Primarily deployed in African and regional mail infrastructure.
Internal blocklist maintained by InterServer hosting. Primarily affects deliverability to addresses hosted on InterServer infrastructure.
Independent DNSBL listing spam sources and open relays. Used by a subset of mail server operators and SpamAssassin configurations.
Minimalist DNSBL populated exclusively from mail sent to S5H.net trap addresses. Automatic listing and expiry, no human intervention.
Lists bogon IP ranges: unallocated IANA ranges and reserved space that should never appear as source addresses on the public internet. Not a spam list.
Lists known Tor exit nodes. Used by some mail servers to flag or reject mail from anonymous Tor network infrastructure. Not a spam list.
Formerly listed open relays (RELAYS) and uncertain sources (UNSURE). Not actively maintained since mid-2010s. Some legacy SpamAssassin configs still query it.
Swiss network operators group blocklist with inconsistent maintenance. Primarily historical relevance to Swiss email infrastructure.
Listed botnet and malware IPs. Operated by independent researcher Janit0r. Shut down in 2019. MTA queries return NXDOMAIN.
Phishing and spam sources blocklist. Discontinued around 2013. DNS queries return NXDOMAIN. Remove from any active MTA configurations.
Small German independent DNSBL. Discontinued. DNS queries return NXDOMAIN or SERVFAIL.
Internal blocklist from Canadian particle physics lab TRIUMF. Never a widely deployed public DNSBL. No longer maintained.
Small Swiss SMTP blacklist. Discontinued. DNS queries no longer return valid responses.
Dutch anti-spam project DNSBL. Discontinued. No longer operational.
DNSBL zone associated with Kemp Technologies and Spamhaus network infrastructure. No longer actively maintained. DNS responses unreliable.
Blocklist focused on malware-sending and compromised host sources. Discontinued. No longer operational.
Small independently operated DNSBL. Discontinued. DNS infrastructure no longer operational.
Early 2000s independent blocklist from Leadmon.net. Long discontinued. Historical reference only.
MAPS relay blocklist family (RBL, RSS, DUL). Acquired by Trend Micro. Public free DNSBL service discontinued. Enterprise subscription only.
Small independent DNSBL. Discontinued. Historical reference only.
Habeas sender certification and reputation list. Acquired by Return Path. Certification program discontinued.
About the Author
Alaa · LinkedIn
Email infrastructure specialist with 8+ years of hands-on experience in SMTP, deliverability, and email verification. I’ve configured and troubleshot mail systems across Postfix, Exchange, and cloud relays, managed IP reputation and warmup campaigns, and built verification pipelines processing millions of addresses. My work spans DNS authentication (SPF, DKIM, DMARC, BIMI), bounce handling, blocklist monitoring, and compliance frameworks including CAN-SPAM and GDPR. I write every article on SMTPedia to give email professionals, developers, and marketers the accurate, RFC-grounded reference they need.
About SMTPedia
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