In general, the subject matter described in this specification can be embodied in methods, systems, and program products. A score for each of a plurality of authors of posts submitted to a server system is determined. The score for each individual author in the plurality is based on a score of one or more authors in the plurality that have requested to subscribe to a stream of posts that the individual author submits to the server system. A particular post submitted by a particular author in the plurality is received at the server system and from a computing device. A score is assigned to the particular post based on a score of the particular author. The particular post is transmitted from the server system to computing devices that are associated with authors who have requested to subscribe to posts by the particular author.