The most recent update to Inbox, 1.49, has made a minor tweak that could be a lifesaver. Now when you make a response to an email via a notification, you have a window to undo sending the email in the same notification. So if you notice a misspelling, see the wrong recipient, or change your mind just a moment too late, now you have a chance to pull things back, just as you would on the desktop site or app.
We gave the APK a teardown. But, so far this looks to be the only difference in 1.49. Even the full (and brief) changelog can testify:
• You can now undo an action taken inside a notification.
There's nothing special to set up or change to get it to work, it's an automatic part of the new update that you'll see the next time you respond to a message via an Inbox notification. You can pick up the latest version over at Google Play, or via APK Mirror.