Buttondown's email subscription spam firewall

This is interesting. I've been using my transactional email provider (Sendgrid) to manually [0] send newsletters to ~10k subscribers -- essentially the active accounts -- but I've noticed that my response rate has been super low the last year or so (relatively), so I'm wondering if my domain rating has taken a hit. This firewall is interesting. Maybe I should switch to a newsletter provider like this instead of sending as transactional email? I figured it wouldn't scale and that it'd bite me eventually...

[0]: https://github.com/keygen-sh/keygen-api/blob/master/lib/task...

p.s. it's a pet-peeve of mine when docs subdomains have no obvious link to the top domain!