[Remail] RFC: "transport" encryption type

[Konstantin Ryabitsev]

Hello:

Remail currently provides 2 encryption options: s/mime and pgp. How 
about adding a third option called "transport" that would basically 
delegate the task of encryption to the transport layer (effectively, 
sending cleartext mail to those subscribers). There are cases in which 
this would make sense, for example:

- the email is delivered to an inbox on the same infrastructure managed 
  by the same people who have access to the remail encryption keys
- the email is delivered to an inbox over an encrypted SMTP+TLS session 
  and the provider has the user's private keys anyway (e.g. s/mime 
  option set up via GSuite, where email is decrypted on the Google side 
  of things)

What do you think?

-K