How to Send and Receive Confidential Email in Gmail
If an email contains sensitive information, and you want to control who can see it, you can use confidential mode. Confidential emails cannot be forwarded, copied, or downloaded, and you can also give an email an expiration date, after which it can no longer be accessed.
It opens up, with the message inside a confidential text box. You can also see that the options to forward, print, copy, and download the message are unavailable.
Finally, it's important to note that you can send a confidential email to someone who doesn't use a Gmail account, although it won't be as easy for them to view it. Instead of seeing the confidential message within a text box, they'll instead be required to click a link to open the message in a browser window.