Sometimes you accidentally tap the screen and send, archive, delete a mail on your phone. Enable the option to confirm before deleting on Gmail for Android, so a confirmation message appears before any action happens.
Follow these steps:
1. Open "Gmail" app
2. Go to "Settings" by either hitting Menu Button or the three dot icon
3. Select "General Settings"
4. In the "Action Confirmations" settings, you have 3 options: Confirm Before Deleting, Confirm Before Archiving, Confirm Before Sending
5. Mark the items you need