SORBS Spam Blacklist: What Is It?
Understand what the SORBS DNS-based blacklist is, how IPs end up listed, and what to do if your address appears there.
What Is the SORBS Blacklist?
SORBS (Spam and Open Relay Blocking System) is a DNS-based blacklist that tracks IP addresses associated with spam, open relays, open proxies, and other abusive behaviors. Email providers and spam filters can query SORBS to help decide whether to accept or reject incoming messages from a given IP.
Like other DNSBLs, SORBS is one piece of a broader email reputation ecosystem. Being listed can cause mail to be flagged as spam or rejected outright by some receiving systems, while remaining unlisted does not guarantee clean delivery.
How IP Addresses Get Listed on SORBS
IPs are usually added to SORBS when they send large volumes of unsolicited mail, operate as open relays or proxies, or show other indicators of abuse. This behavior may result from compromised servers, misconfigured mail systems, or intentionally malicious activity.
Shared hosting environments and poorly secured mail servers are common culprits: one compromised customer or misconfigured site can impact many domains that share the same outbound IP. Monitoring your outbound mail patterns and server logs helps you detect and correct problems before they harm your reputation.
Checking Your Status and Requesting Delisting
If users report that your emails are bouncing or landing in spam, checking major blacklists—including SORBS—can reveal whether your IP has been flagged. Use a blacklist check tool or SORBS’s own lookup interface to review your status and any associated evidence.
To resolve a listing, first fix the underlying issue: patch servers, close open relays, secure accounts, and stop any abusive traffic. Once you are confident the problem is resolved, follow SORBS’s delisting instructions, which may include submitting a request, acknowledging the cause, and agreeing to maintain better practices going forward.