With Google Sync for iOS, the default setting when you delete email in your iOS Mail app is that Gmail will archive the message and not delete it.
A new option “Delete Email As Trash” is now available. When you Enable “Delete Email As Trash” for this device, pressing Delete in your iOS Mail app will delete that email from your device and send it to your Gmail Trash.
Finally!
My biggest complaint with using Gmail with an external client (eg Mail on an iPhone) is that delete doesn’t really delete – it archives. I don’t want it to archive, I want it to delete!
Sure, using the Gmail app or the browser view works around this, but that really doesn’t solve the problem.
Now, finally, you can configure the action from the Google Sync settings page on your mobile device.