Google is finally rolling out Gmail features that were first Web-only, to its mobile verticals as well. One of the biggest features that arrived in 2015, after years of testing, was Undo Send - the ability to recall an email after tapping send button. This feature was a fresh welcome for those that managed to send erroneous mails, and previously had no way to recall whatsoever. In November 2016, it was then made available to iOS users, and now, it has finally arrived on Gmail for Android as well.
The feature was first spotted by Android Police, and it seems to have arrived with version 8.7 for Android users. It works in a similar manner like its desktop variant, but there is no functionality to manually set the time slot for cancellation, or even disable it. Once you send a message, a snackbar at the bottom shows you a 'sending' message with the option to cancel it while it's sending. Once it's sent, Gmail then shows the 'sent' message with a new option to 'undo' it as well. This is showing up for all users on Gmail version 8.7, and if you can't see this feature, head to the Play Store and see if there is a pending update.
As mentioned, 'Undo Send' was in Gmail Labs for many years since it was introduced in March 2009. It finally arrived on the Web in 2015, and has finally made its way to Android now. Another feature that Gmail recently introduced on mobile was Confidential Mode, which essentially allows user to send emails to others that will self-destruct after a point of time.