Google add new feature to Gmail,you can access it by using google lab feature.It allow users to recall e-mail that they have sent by mistake. This feature work on a technique by grabbing email which have sent by mistake.
The option of Undo Send will came that lets you abort the delivery of any Gmail message within moments of sending it. Undo Send can be activated from the Settings/Labs tab in Gmail.

After activation of the feature, a new ‘Undo’ link will appear next to every sent e-mail confirmation. When clicked, ‘Undo’ will take you back to the composing window and confirm the retrieval of the e-mail.
However, ‘Undo Send’ doesn’t really recall a message that has been already sent. The feature only holds e-mails in a queue for five seconds, giving you time for second thoughts — though some already argue that this is not long enough.

This application was announced by official google blog in its blog post