Just right after rolling out the email preview feature for YouTube videos, Flickr and Picasa photos and Yelp reviews, the Gmail Labs is introducing a new feature again. This time, the feature lets users undo sent email which are not supposed to be sent yet, or emails which contain errors.

Actually the new feature is turning a Gmail bug into well, a useful feature. When sending messages, Gmail usually has a 5 second delay. Meaning the Gmail server does not immediately process the message and transmit to the recipient. So, if users click on the Undo button within that 5 second delay after hitting the send button, Gmail can stop processing it giving the senders enough time to make some changes to their messages.

It’s a pretty simple feature really, and yet users who re-read their messages after sending it can probably save them time and humiliation.

As for us who don’t bother re-reading a sent message, well that five second delay would remain a Gmail bug.

Turn on this feature at the Gmail Labs tab on the Settings of your Gmail account. After activating the feature, you’ll see the “Undo” button the next time you send a Gmail message.