A system and method provides a computer-implemented messaging service. Users subscribe to message channels. A message queue buffers messages to a router. The router determines whether characteristics of a first message match criteria specified in subscription requests, and may route the first message to one or more sending agents based on modes of communication specified in the subscription service requests. The sending agent(s) generate a second message formatted for the specified modes of communication based on the first message. Message load balancing, message queuing, message routing, and message sending services may all be independently scaled to adjust for demand.