Unintentionally sending an email is a very annoying thing. Fortunately, users of Gmail for Android now have access to a cancel button.
How to cancel an email sent by mistake on Gmail
Version 8.7 of the app adds the feature Cancel, which means that if you accidentally hit Send, you can quickly recall the e-mail by tapping “Cancel”, which appears right after at the bottom right of the screen.
Tap "Cancel" and you will be redirected to the compose screen, allowing you to change your email or delete it entirely.
You will have a few seconds to cancel it but if you know how to do it you will have the timeliness to carry out the operation and thus avoid sending an email by mistake with Gmail