A messaging system is described. The system includes a memory device. The system also includes a receiver configured to receive a message subscription from a user and to store the message subscription on the memory device. The message subscription is based on a message aggregate characteristic which includes an aspect other than textual content and bibliographic content. The system also includes a subscription engine configured to determine a published message in response to receiving the message subscription. The published message satisfies the message aggregate characteristic. The subscription engine is also configured to provide an indication of the published message to the user.