Spam Uniform Resource Identifier Real-Time Block List (SURBL)

What is it?

What is it?

The Spam Uniform Resource Identifier Real-Time Block List (SURBL) is a system used to detect and block spam emails based on the presence of URLs (Uniform Resource Locators) within the email content. SURBL maintains a database of known spam URLs and provides real-time lookups to identify and filter out spam messages containing these URLs, helping to improve email security and reduce the impact of spam on recipients.

Key points to remember

Key points to remember

  • URL-Based Filtering: SURBL focuses on identifying spam based on the presence of URLs within email messages. It checks whether the URLs embedded in the email content match entries in its database of known spam URLs, typically associated with malicious or undesirable content.

  • Real-Time Lookup: When an email is received, the server performs a real-time lookup against the SURBL database to determine if any URLs in the message are flagged as spam. If a match is found, the email may be flagged as spam or subjected to additional filtering measures to prevent delivery to the recipient's inbox.


  • Collaborative Database: SURBL relies on contributions from a network of users, organizations, and security researchers to maintain its database of spam URLs. Contributors report and submit URLs found in spam emails, which are then added to the SURBL database for detection and blocking purposes.


  • Integration with Spam Filters: SURBL is often integrated with spam filtering solutions and anti-spam systems that ISPs, email providers, and organizations use to enhance their spam detection capabilities. By leveraging SURBL data, these systems can identify and block spam emails containing malicious or suspicious URLs.


  • Effectiveness and Limitations: While SURBL can effectively detect and block spam emails with known malicious URLs, it may not catch all types of spam, especially those using new or previously unseen URLs. Additionally, legitimate URLs may occasionally be flagged if they resemble known spam URLs.

Example of Use

Example of Use

  1. Email Security Solutions: Email security products and services, such as anti-spam gateways and email filtering appliances, incorporate SURBL into their spam detection and prevention mechanisms to scan incoming emails for suspicious URLs and block spam messages before they reach users' inboxes.


  2. ISP Filtering: Internet service providers (ISPs) and email hosting providers utilize SURBL to augment their spam filtering capabilities, helping to protect their customers from receiving spam emails containing harmful or fraudulent URLs.

Find and verify emails for free