1. A method comprising: receiving, by a processor, data of an event stream, each event in the event stream to be delivered electronically to a client device over a network; storing a data structure indicative of one or more events in the event stream that are not yet delivered to the client device, wherein the event stream is assigned a unique conversation identifier, and wherein the data structure includes: one or more entries corresponding to the one or more events in the event stream, wherein each of the one or more entries includes a communication number, a recipient identifier associated with a recipient, and a status; and content of a most recent event of the one or more events in the event stream labeled with the communication number for the most recent event and a sender identifier associated with the most recent event; retrieving, by the processor, from the data structure, data indicative of a current state of the event stream, wherein the current state of the event stream includes a number of events not yet delivered to the client device and the content of the most recent event in the event stream; and sending, by the processor, the retrieved data indicative of the current state of the event stream to the client device.