A notification service that efficiently scales to the number and variety of notifications and users being serviced. The notification service is separated into three general functional components. A listener component receives a notification in a network format suitable for transmitting the notification over a network. The listener component translates the notification into an internal processing format used by the notification service. The notification is then forwarded to a routing component that determines a category associated with the notification, and performs a set of one or more operations on the notification based on its category. Finally, the notification service is forwarded to a delivery service for delivery of the notification to the notification sink. The listener component, the routing component, and the delivery component may each be scaled in order to adjust for current processing loads using load balancing functionality.