A server is disclosed for filtering e-mail messages. The server receives requests to retrieve e-mail messages on behalf of a client and then retrieves e-mail messages from a mail server on behalf of the client. The server then filters the e-mail messages based on one or more rules and transfers the filtered e-mail messages to the client. In addition, the server continues to filter the e-mail messages after the client has disconnected from the server. In one embodiment of the invention the e-mail message recipient is sent a notification by the server indicating that messages have been filtered. The recipient is then able to scan the filtered messages and insure that the messages have been filtered correctly. In another embodiment, a third party scans the e-mail messages on behalf of the e-mail user to make this determination. Also disclosed is an e-mail filter comprising an application programming interface and a plurality of dynamically loaded rule modules adapted to interface with the API. The rule modules are activated and deactivated based on usage. Specifically, rule modules which have not been used for a predetermined period of time are deactivated. In addition, different rule modules are assigned different weighted values based on the probability that the rule module will accurately filter e-mail messages and/or on the content of the e-mail messages.