After Google launches an update for Gmail, you'll be able to install an "expired" time from an email, which will make the email disappear from your inbox and recipient.
In addition, you can also email in "Secret Mode" which will prevent the recipient from sending that email to anyone else, copying the email, downloading or printing it, as Mashable mentions.
Later, you will also be able to add an extra layer of security for highly sensitive emails. You can ask the recipient to confirm their identities using the code sent to their email or login before viewing the contents of the email.
In addition to some security features, Google will also add features that they have embedded in Inbox. One such feature is Snooze, which allows you to remove emails from your inbox until a certain time. Google will also introduce the Smart Reply feature in this update.