Various embodiments provide session-based filtering to filter messages in a cooperative manner between a client and a service provider. In at least some embodiments, a service provider can establish a messaging session with a client and deliver messages to the client. The client can implement various client-side techniques to filter some of the messages based on various client designated criteria. The service provider can obtain feedback from the client indicative of one or more of the delivered messages that have been filtered. The service provider can dynamically create a session-based list based on the feedback and use the list during the session to block messages on the server-side according to the client designated criteria. When the session concludes, the session-based list can be discarded. In this manner, message filtering can occur without persistent storage of state data for the filtering at the service provider.