Does PrivacEmail.com and/or its partner Hush Communications have a "back door" that can be accessed by authorities?

No. All PrivacEmail messages, including attachments, that are sent between PrivacEmail.com users are completely encrypted. There are no "back doors."

Note: You can send unencrypted messages by de-selecting the "Send securely" checkbox in your PrivacEmail account. Also, messages sent to non-secure e-mail addresses are not encrypted.