An instant message delivery system includes a network node with a packet queue. The packet queue stores packets containing instant messages. When the system detects network congestion, it merges two or more packets where possible to make a single packet. In particular, when two or more data packets contain instant messages with the same recipient, the system merges the data packets into a single data packet with multiple instant messages. When two or more data packets have instant messages with the same recipient and the same sender, the system merges the data packets into a single data packet and further merges the instant messages into a single instant message containing more than one message body.