Described is a pipeline for handling notification messages sent to a mobile messaging message (e.g., SMS or SMTP) recipient, and handling a reply to that notification message, including correlating the notification message with the reply. An engine receives a notification message, and for a notification message to which a reply is possible, maintains state data for use in correlating a received reply with the notification message. The state data includes metadata that indicates that text or code data is expected in any reply. For a reply providing code data, the engine calls a selected URL corresponding to the code. To facilitate message delivery, the engine may format the notification message, including shortening a URL of the message, and/or splitting a longer notification message into shorter notification messages.