Gmail confidential mode launching on by default on June 25 2019

Confidential mode provides built-in information rights management controls in your emails by allowing senders to create expiration dates and revoke previously sent messages. Because a sender can require additional authentication via text message to view an email, it’s also possible to protect data even if a recipient’s email account has been hijacked while the message is active. Additionally, with confidential mode, recipients don’t have the option to forward, copy, print, or download their content or attachments.

References:

Google Announcement

Protect Gmail messages with confidential mode

Send & open confidential emails