As you already know, Gmail has been redesigned and its changes are not just about its appearance. OR Google e-mail service, has acquired new features and is going to gain more with the weather. For example, we'll soon see a predictive text feature that will allow you to select suggested words to automatically populate a message.
But for now, the new feature that's already available is the confidential operation of Gmail or Confidential Mode.
With confidential Gmail, the email you send will expire after a set period of time. By default, this time period is 1 week, but you can set a different expiration date.
A message with confidential content has an extra level of security: The recipient will have to enter a password sent to them via SMS to read the message. The availability of this particular feature is not available globally, so not everyone who has confidential mode in Gmail can use it. In Greece it works without any problem.
Let's see how it works:
Open Gmail and click on new message in the upper left. At the bottom, you'll see a new padlock icon with a clock. Click
A new window opens where you can set the end of the message.
There are predetermined time periods. one day, one week, one month, one year and five years.
To add a password, select the "SMS Password" option. If your message has more than one recipient, you must enter a phone number for each recipient. The SMS password is the password that your recipient needs to unlock the message that will be sent to the phone number that you add, so make sure it is correct.
When you tap Send, and use the SMS function, a new window opens to add the recipient's phone.
After adding the phone number, you can send the message.
That's it. You can send the message and if you want, you can undo it within 30 seconds. If you later understand that you have sent the message to the wrong person, you can click the Callback button on the sent message and the recipient will not be able to open it. 
Confidential emails do not open within Gmail. You will receive the message in Gmail, but when you open it, you will need to click a second button to view the message in a new tab (View the email, as shown in the image above).
If you block access to a message, the email will not disappear from the recipient's inbox, however, when it clicks on the View the email link, Gmail will inform it that it does not have access to the message.
Access to a message is abolished indiscriminately for all recipients of the message. You can not revoke access to a person and allow others.
