The current version of PreVeil Email only shows end-to-end encrypted messages that have been sent to you by other PreVeil users. The mobile app and browser web app do not show messages from Gmail, Yahoo, Hotmail, or any other email provider.
If you add PreVeil to your Apple Mail or Outlook client you will see a new mailbox for your PreVeil account. You can use this mailbox to send and receive encrypted messages using your PreVeil account. Adding a new encrypted mailbox will not do anything to your existing emails or mailboxes.