What it is
DroneBL originally emerged from the IRC community to block compromised hosts used for DDoS attacks on IRC networks. It has since expanded to cover open proxies, botnet command-and-control servers, and compromised hosts more broadly. Some mail server operators use it as an additional signal for identifying compromised sending IPs.
How it affects SMTP delivery
DroneBL is used in some MTA configurations and composite DNSBL tools. It is not as widely deployed in email filtering as Spamhaus or SpamCop, but a DroneBL listing typically indicates a genuinely compromised host, which is a significant deliverability concern.
What causes a listing
Listings occur when an IP is identified as a compromised host (zombie), open proxy, or botnet drone through DroneBL's detection methods.
How to get removed
Submit a removal request via the DroneBL portal at dronebl.org. Manual review is required and typically takes 24-72 hours.
For the full reference catalog, see the email blocklist directory.
Delisting process in detail
DroneBL specifically tracks IPs identified as part of botnets (drone armies used for coordinated attacks, spam sending, or malware distribution). Delisting is handled at dronebl.org through the removal form. Because DroneBL listings usually indicate active compromise, delisting requires documented evidence that the infection has been remediated: malware removed, patches applied, credentials rotated, and outbound scanning shows no continued attack traffic. Automatic decay occurs when the observed botnet activity stops, typically within 14-30 days. DroneBL is aggressive and delisting can require significant remediation documentation.
Prevention practices
DroneBL prevention is entirely about server security. Ensure sending servers are patched, isolated from other network services (dedicated mail-sending hosts, not shared with web or SSH access from untrusted sources), and monitored for anomalous outbound traffic (excessive TCP connections, unusual DNS queries, connections to command-and-control infrastructure). A DroneBL listing on a mail-sending IP is a strong signal that the host is compromised and should be taken out of production immediately for forensic investigation.
Common listing causes
DroneBL listings almost always indicate active compromise: attackers have gained control of the host and are using it for coordinated attacks. Common vectors include unpatched web applications on the same host as the mail service, weak SSH credentials that have been brute-forced, and compromised customer accounts on shared hosting used to launch attacks against third parties. Legitimate senders rarely appear on DroneBL by accident; a listing should trigger immediate security response.
Related blocklists
Botnet-tracking blocklists include DroneBL, Spamhaus Botnet Controllers list, and various commercial threat intelligence feeds (Cisco Talos, Team Cymru’s TCP-33 feed, Mandiant/Google Threat Intelligence). Enterprise mail administrators typically monitor DroneBL alongside Spamhaus XBL for compromised infrastructure detection. A DroneBL listing is one of the strongest signals that a host should be taken out of production; the mail deliverability implications are secondary to the security incident.
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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