Known Issues

Messages in the sent folder appear not to be encrypted although server-side protection is enabled

The message in the sent folder are in fact stored encrypted on the IMAP mail server.

However, when your mail client stores the message in the sent folder after it has been sent, it cannot know that the mail server encrypts the message, but assumes that it is stored unchanged. Therefore, in order to reduce traffic, it does not download the message again, but shows you the original plain text message.