Last month, Google introduced an "Undo Send" option for all Gmail users, allowing anybody to recall messages up to 30 seconds after sending them. However, if 30 seconds isn't enough time for you to spot an error (or realize that that's actually a totally inappropriate thing to say to your boss), then you might want to try Dmail: a Chrome extension that allows Gmail users to revoke access to an email any time after sending. You can even set a self-destructing timer that automatically makes an email inaccessible an hour, a day, or a week later.

Dmail doesn't actually delete messages from users' inboxes

Perhaps the most useful thing about Dmail is that it works even if not installed on a recipient's computer. This is because the service doesn't actually delete messages from users' inboxes, but instead encrypts and decrypts them on demand. Users who receive a Dmail and don't have the extension installed are shown a "View Message" button that opens the email in a new tab. (If they do have Dmail installed, then the message is just shown within Gmail.) After a sender revokes access to an email — either manually or automatically — recipients are informed that "this message has been destroyed and is no longer available."

Grid View How Dmail appears in Gmail's interface.

How a message sent with Dmail looks to a user without the extension installed.

And how a received message looks in a new window.

Messages sent with Dmail can be destroyed at any time.

Once destroyed, the recipient can no longer read them.

Dmail's Eric Kuhn explains to TechCrunch that whenever a user sends a message with the service, it's encrypted locally on their machine with a standard 256-bit algorithm. "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," says Kuhn. "Neither Gmail nor Dmail servers ever receive both the decryption key and encrypted message. Only the recipient and sender can read the email legibly."

If you revoke access to an embarrassing email, you'll still have to explain why

It's a neat trick, but it's not quite the same as deleting a sent email remotely. This means that using Dmail as a security measure makes more sense than as a face-saving "Undo Send" option. After all, if you do revoke access to a message a few minutes after sending, you'll still have to explain to the recipient what was so regrettable about the email in the first place. (The excuse "Oh, I'm just testing this new service out" only works the first couple of times.)

Still, Dmail is slick and easy to use, and the team responsible (part of social bookmarking service Delicious) have plans to extend its functionality, rolling out support for iOS and Android later this year, as well as hopefully adding a "self-destruct" functionality to document attachments. They also have plans to make Dmail a freemium service, with extra options for paying businesses and power users. Until then you can try the Dmail beta for free here.

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