A computer-implemented method for preventing spam emails from a share site includes providing a network-based computer system to enable users to set up share sites and to send emails from the share sites, detecting potential spam emails based on one or more spam detection rules, identifying false positive emails in the potential spam emails based on one or more false alarm reduction rules, removing false positive emails from the potential spam emails to produce a list of verified spam emails, identifying a sender of the list of verified spam emails as a spammer, and prohibiting the spammer from sending emails from one or more share sites owned spammer.