To streamline checking for new messages, Postbox will store your account passwords in a hidden file so it won't have to ask every time. You can use a Master Password to encrypt this password database to enhance security, and to prevent the downloading of new messages to your computer. You will be required to enter the Master Password each time Postbox launches, but it will be remembered for the remainder of the session.
Note: The Master Password does not prevent access to email messages, attachments, contacts or other information.