A system and method for multivariate testing of messages to a subgroup in a one-to-many messaging platform. A client text message is generated for transmission to a number of users via one or more messaging services. A subset of users is defined according to one or more attributes of the text message or the users, and the client text message is transmitted only to users in the subgroup. The transmission is analyzed for performance metrics, such as actions or reactions by users in the subgroup, and based on the performance metrics, the message is optimized for transmission to the larger group of users. Optimization happens rapidly.