Microsoft Notification Protocol (MSNP) is an instant messaging protocol developed by Microsoft for use by the .NET Messenger Service and the instant messaging clients that connect to it, such as Windows Live Messenger, its earlier incarnations MSN Messenger and Windows Messenger, and Microsoft Messenger for Mac. Third-party clients such as Pidgin and Trillian also communicate using the protocol. MSNP was first used in a publicly available product with the first release of MSN Messenger in 1999.
