System and Method for Tracking Messages in a Messaging Service

A system, server and a method for processing messages received at a server device in a network are provided. The method comprises: for a message being transmitted from a first account associated with a client device to a second account in the network, receiving a message event associated with the message at the server; determining whether the message event is associated with an existing conversation involving the first account, and if so setting a sequence number associated with the message event to a value incremented from a current sequence number associated with the existing conversation, otherwise setting the sequence number to a value to track a new conversation; and sending the sequence number to the first user account.