H ELECTRICITY
H04 ELECTRIC COMMUNICATION TECHNIQUE
H04L TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
51/00 User-to-user messaging in packet-switching networks, transmitted according to store-and-forward or real-time protocols, e.g. e-mail
H04L51/21 Monitoring or handling of messages
H04L51/216 Handling conversation history, e.g. grouping of messages in sessions or threads