> This is fairly normal in today’s world of email providers, and one of the reasons it can be painful to manage your own SMTP server, right?

Yes. Silently discarded e-mail is the worst thing that can happen because you can't detected it as a sender. Your message reaching the spam folder is bad, but not as bad as getting silently discarded.

The best among the bad options is probably getting rejected with the SMTP return code 550 along with instructions how to delist in the return message.