An IP address may appear on the Spamhaus CSS list due to a variety of reasons including spam activity, malware infections, compromised systems, poor sending practices, or even technical issues at Spamhaus. Being listed negatively impacts email deliverability and sender reputation. The key is to identify the underlying cause, remediate the problem, and then request delisting. Proactive monitoring, following email deliverability best practices, and avoiding sudden sending volume increases are essential for preventing future listings.