On June 25, 2019, this feature will become generally available and your users will have the option to send emails with confidential mode. At launch, confidential mode will be set to default ON for all domains with Gmail enabled, unless you choose to disable this feature. With confidential mode, recipients dont have option to forward, copy, print, or download content or attachments. When a user sends a confidential message, Gmail replaces the message body and attachments with a link. Only the subject and body containing the link are sent via SMTP. This means that if your users send or receive messages in Gmail confidential mode the Vault will preserve, search and export confidential mode messages.”]
Source: https://workspaceupdates.googleblog.com/2019/05/gmail-confidential-mode-launching-on-by.html