GMail keeps getting feature rich day in day out.
I noticed this update after GMail for web (chrome browser) asked to be refreshed after installing some updates.
The confidential mode allows for emails being sent to be read-only. By read-only, recipients will not have the option to forward mails, download or print them.
There is more...
The option to set expiry dates for emails, after which the recipient and for the matter anyone else will no longer have access to the email in question.
A very simple but intriguing feature. Did not know I needed this, until it existed.