This chime was the new-mail alert in MSN Messenger, Microsoft's dominant chat client of the early-to-mid 2000s, telling Hotmail users an email had landed while they chatted. As MSN faded, the sound survived through nostalgia compilations, Y2K aesthetic edits and reaction memes about ancient technology. It now sits alongside the modern Discord notification as shorthand for an incoming message, and like any classic ding sound effect it works because a generation instantly recognises it.