Sensitive Data should always be handled with care. Gmail is now rolling out a Confidentiality mode for whenever we send email that contain personal data or information.
As this feature is currently still in Beta, your admin does have to opt in in order to activate this feature for the domain. Once activated the user in your domain can select confidential mode from within their compose window.
This sets an expiry date for the email and makes sure the email in question can not be downloaded, forwarded, or printed. In addition to this you can set a passcode for the email in order to enable the recipient to open this securely.
The admin and Vault user will still have access to the email according to the set retention rules.