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Spamhaus CSS Component of the SBL

What is the Spamhaus CSS?
The Spamhaus CSS list is an automatically produced dataset of IP addresses that are involved in sending low-reputation email. CSS mostly targets static spam emitters that are not covered in the PBL or XBL, such as snowshoe spam operations, but may also include other senders that display a risk to our users, such as compromised hosts. CSS lists both IPv4 addresses (/32) and IPv6 addresses (/64). CSS listings are influenced by:
  • Email showing indications of unsolicited nature;
  • Broad-spectrum aggregated views of email deliveries;
  • Having poor list-hygiene;
  • Sending out bad email due to a compromise (compromised account, webform or CMS);
  • Other indicators of low reputation or abuse.
CSS listings are based on a wide range of inputs and are always the result of multiple events and heuristics.

Why is my mail being blocked?
Spamhaus is a reputation data producer. The actions taken based on our data will differ amongst email/internet service providers. It is up to the provider to decide how to treat IP addresses listed in the CSS.

If you are authoritative for an IP address and you believe the issues that caused the listing have been solved, you can request a delisting.

How can I use the CSS?
The CSS dataset is part of our SBL, return code, and thus part of ZEN. If you use ZEN, you are automatically using the CSS dataset. Use of return codes varies by application.
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