«When a ProtonMail user sends an expiring message to another ProtonMail user, it looks like a regular email in the inbox. After the message expires, it is automatically deleted from the inbox and the sender’s outbox. In Gmail’s current implementation, it sounds like Google simply generates an email with a link. The message behind the link disappears after a while, but not necessarily the intermediate email. It’s also worth noting that Google doesn’t mention end-to-end encryption anywhere. A “confidential” message doesn’t have to be encrypted. It’s likely that Google could still see the content of that message and comply with warrants».

Source : Google is testing self-destructing emails in new Gmail | TechCrunch