nAnswer:
The PGP keyserver network
nA
distributed network of key/cert databases that can be queried by anyone.
nStarted
as a mail-based server network
nMail
in your key, it gets added to the server’s keyring.
nMail
in a request for a key, you get sent back a subring containing every key that matched
your query.
nServers
updated each other by passing around “add key” requests.