In general, even DKIM and a clean domain isn't a safe indicator of non-spamminess. It doesn't take much effort nor cost for a spammer to get a new domain, set u

In general, even DKIM and a clean domain isn't a safe indicator of non-spamminess. It doesn't take much effort nor cost for a spammer to get a new domain, set up DKIM/etc correctly and then start spamming, and those emails would appear as "clean" as yours do. Therefore they use extra heuristics including the source IP ranges. Plus in your case your current mail tester result suggests you don't even have DKIM set up, so as of right now there's literally no way for a recipient server to tell your email apart from a spammer impersonating you. (to be clear I'm not defending the practice, just explaining my understanding of the current situation)