Yeah I really will give people a pass here. The state of email is one of the worst collective mistakes I think we've made.
You can literally be an expert in everything relevant - and your mail will still not get delivered just because you're not google/mailgun/etc.
I was trying to do a very simple email-to-self use-case. I was sending mail from my VPS (residential IP not even allowed at all) which was an IPv4 i'd had for literally 2+ years to exactly only myself - my personal gmail. I had it all set up - SPF, DKIM, TLS, etc etc. And I was STILL randomly getting emails sent directly to spam / showing up with the annoying ! icon (grates on my sensibilities). I ended up determining - after tremendous, tremendous pain in researching / debugging - that my DKIM sigs and SPF were all indeed perfect (I had been doubting myself until I realized I could just check what gmail thought about SPF/DKIM/etc. It all passed). And my only sin was just not being in the in-crowd.
Incredibly frustrating. The only winning move is not to play. I ended up just switching from emails-to-self to using a discord webhook to @ myself in my private discord server, so I get a push notification.
And this was just me, sending to myself! Low volume (0-2 emails per WEEK). Literally not even trying to actually send emails to other people.