A method, system, and computer program product for processing email messages rescans emails messages that have already been scanned for spam and delivered to user inboxes with updated spam detection rules. This increases the accuracy of spam scanning and reduces the need for users to submit missed spam in emails that was not detected at the time the emails were received, but would subsequently be detected with newer anti-spam rules. A method of processing email messages comprises receiving email messages in a local inbox or in an inbox on an email server, or both, the received email messages having been scanned using spam detection rules to determine whether or not they include spam, obtaining updated spam detection rules, and rescanning at least some of the received email messages using the updated spam detection rules to determine whether or not they include spam.