A method and system to maintain lists of IP addresses for detection of email spam are described. In one embodiment, the method includes receiving email messages from senders associated with Internet Protocol (IP) addresses, filtering the email messages to identify spam, and sending statistics pertaining to the email messages and the identified spam to a server. The method further includes receiving, from the server, IP address lists generated based on the statistics, and filtering new email messages using the IP address lists. The IP address lists received from the server may include a list of safe IP addresses, a list of suspect IP addresses and a list of open proxy IP addresses.