Attachments are automatically encrypted and decrypted within your inbox. Attachments received from incoming outside emails or sent to outside are stored encrypted and cannot be decrypted except by you with the correct mailbox password. When you view your messages, you can decrypt stored attachments immediately within your browser by clicking download.
The Encrypt for Outside Users feature also supports end-to-end encryption of attachments. Attachments sent within an end-to-end encrypted message is saved in the password protected link of the encrypted message.