With the latest version of Galaxkey for Windows, you can  send emails to recipients which can be timed out after a preset time.

The functionality to set the time is available in the Galaxkey Add-in for Outlook.

When you send the email to a recipient, you have the option to set the time until when the email can be accessed. The access blocking functionality is available on all the clients including iOS, Android, Windows Mobile and the Galaxkey Web Access.