When communicating with users of traditional email (Gmail, Yahoo, etc.), by default, letters are sent in unencrypted form. This is done to maintain compatibility. At the same time, all letters in your Beeble account are stored in an encrypted form and are reliably protected.
You can send an encrypted message to a user of another service. To do this, when writing a letter, you must protect it with a password. In this case, the recipient will receive a notification of receipt of the encrypted message and a link to view it. By opening the link and entering the password, your correspondent will be able to read the letter and even reply to it. In this case, all correspondence remains protected.