Can Dovecot reject unencrypted mail?

Hi,

Is it possible to configure Dovecot to reject mail that is not encrypted. In other words:

1. If the user tries to send an unencrypted message from their MUA, the server rejects it.

2. If a third-party tries to send an unencrypted message to the user, the server rejects it.

The end result would be that no mail stored on the server can be decrypted by the administrator.

I am aware that:

• "Encrypted" could mean a lot of things. I'm imagining GPG encryption, but am open to other supported methods.

• This configuration would not suit everyone, e.g. someone posting to a public mailing list :)

Regards, David