Asynchronous multi party messaging is a tangled mess. Top posting is an emergent phenomenon from using the wrong tool (e-mail) for the job. Basically when you

Asynchronous multi party messaging is a tangled mess. Top posting is an emergent phenomenon from using the wrong tool (e-mail) for the job. Basically when you reply to all, you acknowledged which information you have received from and read, and you communicate that to the other participants by transmitting your whole history of your current view of the thread, leaving users the ability to manually do some Paxos if they want to be able to agree on a consistent shared view. Email clients have to recourse to some black magic to merge the threads correctly. If you ever have tried to use email to constitute list of players for a football game where each participant add its name to the list you will quickly find that there are some errors and you got either some missing players or some extra. Because when two people answer simultaneously, the merging is not trivial to do and depends on the mail client. There are also some issues with spam filters or max number of people in conversation which sometimes exclude some people from the conversation. So very quickly history of views can't be merged, and of course it fails silently. There are also probably some accidentally quadratic problems there, but storage is cheap.