What Is the Spamhaus XBL?
A real-time database of IP addresses that are involved in various types of malicious activities on the internet.
The Spamhaus Exploits (XBL) Blocklist is a real-time database of IP addresses that are involved in various types of malicious activities on the internet. These activities include open proxies, worms, viruses with built-in spam engines, and other forms of exploits.
By maintaining the XBL, Spamhaus aims to protect internet users by identifying and blocking sources of spam and malicious software. The XBL is constantly updated, drawing on multiple data sources to ensure its listings are current and accurate. Organizations and individuals can use the XBL to filter incoming traffic, significantly reducing the risk of infections and enhancing overall online security.
XBL Blocklist Tracks IPv4 and IPv6 Addresses
The Exploits Blocklist (XBL) pinpoints compromised IPv4 and IPv6 addresses, identifying legitimate IPs hijacked for malicious exploits. Once substantial evidence indicates an insecure, compromised, or infected device using an IP, Spamhaus automatically adds it to the XBL.
Criteria for Inclusion in the XBL Blocklist
To maintain XBL’s efficacy and prevent circumvention, Spamhaus keeps listing criteria confidential. Common indicators include:
- Malware presence on a device.
- Security vulnerabilities leading to unauthorized access and malicious activities.
- “Free VPN” applications using the device as a proxy.
- Participation in brute-force attacks.
- Frequent identity changes during email delivery.
- Sinkhole connections indicating malware activity.
- Attempts to relay mail with stolen credentials.
XBL listings expire automatically once malicious activity stops.
XBL Blocklist Contains Millions of Listings
The XBL dataset averages 2 million listings, with 650,000 new detections daily. Updated in real-time, combined with other reputation data, it delivers industry-leading catch rates with minimal false positives. Email administrators can leverage this DNSBL to mitigate spam and malicious emails, reducing security risks, infrastructure costs, and human resource demands.
How to Utilize the XBL Blocklist
Maximize Spamhaus data by strategically deploying blocklists during the email filtering process. Use the Exploits Blocklist:
- During the initial connection – against the connecting IP.
- Post-email data acceptance – by checking IPs in the Received chain in headers and by looking up IPs hosting resources in the email body, such as URLs.
For detailed guidance, read this best practice.
Spamhaus Blocklists Have Broad Reach, and are Free
Each Spamhaus blocklist targets specific behaviors; using one alone limits data effectiveness. Spamhaus provides three additional IP-based blocklists for free:
- Spamhaus Blocklist (SBL)
- Combined Spam Sources Blocklist (CSS) (included in the SBL DNSBL zone)
- Policy Blocklist (PBL)
These IP blocklists can be utilized via ZEN, which consolidates these datasets for streamlined querying. While most malicious emails are intercepted during the SMTP transaction, some bad actors invest resources to evade IP detection. To achieve optimal catch rates, domain and hash blocklists should also be employed after email acceptance. Spamhaus offers the Domain Blocklist (DBL) for free to enhance email filtering.
How to Configure XBL
You can leverage the data for connection and SMTP transaction checks through SMTP server configuration. Additionally, utilize open-source tools like SpamAssassin and Rspamd for comprehensive content analysis.
How to Access XBL Blocklist data
The Spamhaus DNSBLs are available at no cost for low-volume, non-commercial users.
How to maintain a good IP reputation
Spamhaus blocklists safeguard billions of mailboxes worldwide. To prevent your email service from being blacklisted, adhere to these best practices:
- Two-Factor Authentication (2FA) – Implement 2FA wherever possible, particularly for accounts with elevated privileges.
- Software Updates – Protect against vulnerabilities by ensuring your software is always up-to-date.
- Restrict Outbound SMTP Traffic – Configure your firewall to permit outbound SMTP traffic (port 25) solely from your mail server’s internal IP address.
- Infrastructure Assessment – Evaluate the reliability of your internet infrastructure providers, such as ISPs.
- Double Opt-In – Prevent spam traps and ensure emails are sent to genuine, interested recipients.
- Proper Configuration – Verify that your hostname and HELO match, and that your reverse DNS (PTR record) points to the same hostname.
While not all these tasks fall under the purview of email administrators, collaboration with network administrators and deliverability specialists is crucial.
How to be Removed from the XBL Blocklist
If your IP is listed on the Exploits Blocklist, visit https://check.spamhaus.org. This platform exclusively manages XBL removals and provides in-depth information along with resolution steps.