The decryption of messages sent to you by others requires your private PGP key. This key is kept safe on our servers and can only be accessed with an additional password that only you, the account user, knows. We, the server operators, do not have this password and therefore no access to your private key.
After logging in to the mailbox.org web interface, you will be prompted to enter your personal Guard password. This will make your private key temporarily accessible for the mail application which can then automatically decode and display any encrypted message you may have received.
If you don’t want to enter the password for each access to encrypted content (emails or encrypted files in drive) you may keep the password stored in your browser for a limited time.