I have a web app I built in Next.js 16 that also has user auth. I want to be able to send transactional emails such as emails such as those for email verification, and possibly receive replies if needed, and since the free account here has a limit and I can't also add DMARC record, I decided to try and add a subdomain and delegate that to CouDNS. But the NS record isn't propagating. Should I just delegate the entire osmanzakir.dynu.net domain? Or is there a way to get the subdomain NS record to work?