email – Why isn’t there a protocol to exchange PGP keys

im curious why there isn’t a defined protocol to retrieve PGP keys from a destination mailserver or if im just not searching with the right parameters.

I imagine a quite simple process like other established processes (AutoDiscovery, etc.)

  1. Sender enters recipients e-mail into the mail client (thunderbird/outlook/whatever)
  2. Mail client resolves the PGP discovery service of that domain via a defined SRV record
  3. If the intended recipient has added a pubkey to his profile the service will answer the request accordingly (otherwise nothing really happens)
  4. The mail client uses the pub key and intransparent to the sender encrypts the message before sending
  5. The end

I mean a database and a very simple web services that takes an e-mail address as a parameter and eventually replies with the corresponding database entry isn’t that sophisticated.

Why hasn’t this been done? Or am I missing a crucial point (except politics)?