An email IP blacklist is a list of internet protocol (IP) addresses that have been identified as sources of spam or malicious emails. These IP addresses are flagged by email providers and added to a blacklist in order to prevent them from sending further emails. Being on an email IP blacklist can significantly impact the deliverability of emails, as they are often automatically filtered out or blocked by email servers. This measure helps to protect users from receiving unwanted or harmful emails, and also helps to maintain the overall integrity of the email system.