Abstract: Techniques are disclosed for processing a workflow campaign. In some embodiments, a message processing service receives a first message that corresponds to a user arriving at a first node of the workflow campaign from a first message queue. The message processing service causes one or more actions associated with the first node to be performed with respect to the user. In addition, the message processing service determines that the first user should be progressed from the first node to a second node of the workflow campaign. The message processing service generates a second message that corresponds to the user arriving at the second node and determines a second message queue that is associated with the second node. The message processing service progresses the user from the first node to the second node by transmitting the second message to the second message queue.

Abstract: Techniques are disclosed for transmitting electronic messages subject to multiple rate limits. In some embodiments, a send-side rate limiter employs a sliding log or other rate limiting technique to determine whether requests to transmit messages comply with rate limits associated with those messages. When the transmission of a message does not comply with associated rate limits, a negative acknowledgment message is sent to a queuing system, causing the message to be reinserted into a queue for later transmission. In addition, delivery rate limits are established for each queue in the queuing system to throttle the delivery of messages to a send service that makes requests to transmit messages to the send-side rate limiter.