I'm not 100% sure about the style tag being the issue but it would potentially line up. If you remove the <style> tag can you save it? It's nothing more than a hunch but I would imagine that Quickbase when sending the email is binding the HTML into their email processor but its the style tag would need to be inserted into the Header to be utilized which is likely causing your issue and potential flag. I've only ever seen rich-text support in-line style using emails.
I ended up re-writing the email template using inline styling and it took. I also learned that email template engines do not support flex-box and other modern styling markup, so that was fun to unravel and fix. Thank you for the response, but I figured my own problems out.
