These refer to the recipient's inability to copy, forward, download, or print content.
If Chief Quimby used Gmail, he'd know about the new mobile Confidential Mode with expiring messages and probably have saved himself quite a bit of trouble getting information to Inspector Gadget. A report stated that Google was working on a new "confidential mode" feature in Gmail that would enable users to send emails that automatically expire. Senders can also do things like set expiration dates for messages so recipients will no longer have access to them.
The new feature is already available without the need to update the app. Gmail did not respond to inquiries when the mode will arrive to iOS devices, but it should hit Apple devices. You can add Confidential settings to an email easily through the 3-dot menu in your app, and once "Confidential Mode" is selected you can set an expiration date, passcode and more. SMS-based passcodes are the only option if your recipient is using a Gmail account - recipients using another email service can receive either SMS or email passcodes.
When sending a confidential email you also have the option of requiring a SMS passcode to open the message.
Users interested in trying out the new confidential mode should look for a new confidential mode icon in the bottom right corner of the compose window.
In April, a brand new design of Gmail was leaked with new features such as snoozing, Smart Reply, and offline support.
You will then have to choose a passcode which can be an OTP on the recipient's phone number, or you can skip it. I sent an email to myself with confidential mode, the attachment was a photo.