Gmail
Emails sent via Gmail can now be set to self destruct upon reaching the recipient, via DmailWikipedia

Google recently released an Undo Send option for Gmail users but now a third-party extension called Dmail makes it possible for users to revoke access to emails even after they have been sent.

By installing Dmail, users will be able to use a self-destruct option, which deletes sent mails after a stipulated period of time. Dmail, created by engineers from Delicious, is available via a specialised Google Chrome extension.

Users will be able to set automated timers to destroy a sent mail, thereby revoke recipients' access to the email.

Dmail web extension for Gmail
A screenshot of the "self-destructing" message, after a recipient reads an email sent via DmailDelicious

The Dmail web browser extension needs to be installed on the sender's computer but recipients can read emails even if they don't have the Chrome extension installed. This service does not physically delete emails on the recipient's side but limits their access to the message.

Emails sent via Dmail are encrypted and get decrypted on the recipient's side. However, if a sender wants to revoke access to a sent email at a later time, the email gets re-encrypted and the recipient gets a "Message unavailable" prompt. The emails are encrypted by a 256-bit encryption algorithm on the sender's computer.

"An encrypted copy of that email is sent to a datastore controlled by Dmail. The recipient of the email is sent both the location of that datastore, as well as a key to view the decrypted message", Dmail product lead Eric Kuhn told TechCrunch.

"Neither Gmail nor Dmail servers ever receive both the decryption key and encrypted message. Only the recipient and sender can read the email legibly," he added.

Upon "destruction" of an email, recipients are notified via a new message that reads: "This message will self-destruct in x seconds/minutes [the time set by the sender]."

Recipients without Dmail can click on the "View Message" button to view the complete email, whereas those with the Chrome extension get to see a message in the same window.

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