What Is an Email Blacklist (DNSBL)?
An email blacklist, also called a DNSBL (DNS-based Blackhole List), is a real-time database of IP addresses and domains that have been identified as sources of spam or malicious email. Mail servers consult these lists to decide whether to accept or reject incoming messages.
How Email Blacklists Work
When a receiving mail server gets an incoming email, it can query one or more blacklist databases to check if the sending IP address or domain is listed. The query uses DNS — the sending IP is reversed and appended to the blacklist's domain, and a DNS lookup is performed. If a record exists, the IP is blacklisted.
Popular blacklists include Spamhaus (SBL, XBL, PBL), Barracuda (BRBL), SpamCop, and SORBS. Each has different listing criteria and removal processes.
Why Blacklists Matter
Being listed on a major blacklist can severely impact your email deliverability. Emails from blacklisted IPs are often rejected outright or sent to spam folders. This affects all email from that IP, including legitimate business communications. Regular monitoring is essential — you may not realize you are blacklisted until emails start bouncing.
Common Causes of Blacklisting
Domains and IPs get blacklisted for sending spam (intentionally or from compromised accounts), operating an open relay, sending to purchased lists with high bounce rates, malware infections that send spam without the owner's knowledge, and lacking proper email authentication ( SPF, DKIM, DMARC).
Frequently Asked Questions
How do I know if my domain or IP is blacklisted?
Use a blacklist checker tool to scan your domain or IP against major DNSBLs. Email Armory's free Blacklist Checker scans against multiple blacklists simultaneously.
How do I get removed from an email blacklist?
First, fix the underlying issue (stop spam, remove malware, fix open relay). Then visit the blacklist's website and follow their delisting process. Some auto-delist after the issue is resolved.
What causes a domain to be blacklisted?
Common causes include sending spam, operating an open relay, high bounce rates, malware infections, and poor email authentication configuration.