Using Gmail's 'confidential mode'


You can set up a time in the future when the email will be deleted (revoked). Clicking on the confidential mode icon at bottom of compose box will bring up this box:


This also prevents the email being forwarded, copied, printed or downloaded.
Gmail allows you to 'remove access' (delete) at any time - go to email in your sent folder to see this option.

You can also encrypt and/or track this email, add password protected attachments or sign the contents.