Overview
SORBS SMTP (Spam and Open Relay Blocking System SMTP) was one of several specialized lists within the SORBS suite, specifically dedicated to detecting open SMTP relay servers. Open relays are mail servers misconfigured to forward email for any sender, making them prime targets for spammer exploitation to obscure message origins.
SORBS was one of the longest-running and most widely deployed anti-spam DNSBL systems, with a suite of purpose-specific lists. SORBS shut down all operations in 2024 after more than two decades of service.
How It Works
SORBS SMTP actively scanned mail servers by attempting to relay test messages through them. Servers that accepted relay connections without authentication were listed. The system ran periodic re-tests, allowing servers that fixed their configuration to be automatically delisted. This proactive scanning approach distinguished SORBS SMTP from passive trap-based lists.
How to Get Delisted
SORBS shut down in 2024, so no removal requests can be submitted. Any SORBS SMTP listings are historical only. If your mail server configuration had an open relay issue, ensure it is corrected to prevent listing on active blacklists. Configure your MTA to only relay for authenticated users and authorized internal networks.