Wish you hadn't just hit send on a email? Gmail's Undo Send feature gives you 30 seconds to put a stop to a regrettable email. Really, all it does delay the sending of any email -- up to 30 seconds. Chrome extension Dmail provides an alternate way to pull back an email, though it doesn't cover all of your tracks.
Dmail adds two items to your Gmail account. First, it adds a line to the Compose window with a toggle switch to enable or disable the extension and, if enabled, a time in the future to destroy the email: Never, In 1 hour, In 1 day or In 1 week. The second item lets you destroy any email you sent previously with Dmail. Click All Dmails at the top of your Gmail inbox to view a list or your emails sent with Dmail, any of which you can open and hit a Revoke Email button.
An email revoked by either method does not erase all evidence of your message. The email will remain in the recipient's inbox, but the message's content will now be encrypted and unreadable. (Or more accurately stated, the encryption key will be revoked for the already encrypted email.) The subject line of a revoked email, however, remains unchanged and very readable, which means an angry email with an ALL CAPS subject line could still cause you trouble.
Recipients do not need to have Dmail installed to read emails. In place of the content of your email, they will see a line about receiving a secure message via Dmail with a View Message button that opens your email in a Chrome tab. Recipients with Dmail, however, can read Dmails right from within Gmail.
While Dmail lets you prevent someone reading an email you sent and gives you up to a week to so automatically, it doesn't erase all evidence, making it better suited for sending the code to a lock or another bit of sensitive information you don't want hanging around forever in someone's inbox as opposed to attempting to take back a hastily worded, ill-tempered email.