honi's comments

Sending emails with no design doesn't mean you send it as plain text. You can still send the HTML version, simply without any markup or styles, and add the tracking stuff there. I think the author is talking more about how it looks rather if it's really plain text email or not.

Send as noreply@ with reply-to header pointing to a valid address.

Do you need to run staging-2 in a complete new cluster? If not, maybe namespaces can be what you need.