Totally. I am not blaming discourse for a second here - you are doing an amazing job and I want to contribute as much as I can.
Here’s what I conclude after several pretty much a week of research - the actual domain, subject, and “from” matter as much as the actual message. I assume that (as expected) html heavy emails (images & links to be precise) are a no-go.
Also, MailJet isn’t really helping as apparently they send bulk marketing emails and transactional ones in the exact same way.
SPF, DKIM, DMARC makes a difference - but probably not as much as said above. At least from my testing, I didn’t have DMARC initially, for example but that didn’t make a difference.
I think I can live with having only the PM and (hopefully) post replies arrive at the primary inbox and have the digest email land at the promotions tab.
To be fair, I think the summary email is a promotional email and it is designed that way. Also, it’s not the most important email. I mean, it gets people back on the forum, but it’s less important than missing a private message or a reply to your topic, in my opinion.