> You mentioned that your emails on Gmail and Outlook initially went to spam, but that you clicked "not spam" on those emails. This action should prevent your emails being flagged as spam for that particular receiver who clicked not spam. Obviously it can't work such that one person clicks "not spam" on an email, and then everything from that sender is whitelisted for everybody. Because then the spammers could just register a single email account, click "not spam" once, and then spam everybody. So my point is, if you test deliverability on email accounts where you have already whitelisted the sender, of course it's going to look like email is delivered.

Obviously I'm aware that me clicking "Not Spam" would not instantly whitelist me in Microsoft's systems, but the hope is that it would influence the spam algorithm somewhat. It doesn't even whitelist me on that account because even after clicking "Not Spam", my emails still went to spam for some time.

> Presumably you and your landlord have already emailed each other in the past, so any anti spam system should allow emails between those addresses to reach their destinations.

Maybe, but my entire university runs on Office365 and I never had any trouble sending to friends and professors there (who have never sent me emails previously).

I'm not really sure what you are trying to say here? Should I have some sort of commercial deliverability monitoring system setup? Do you have insights into what "real email providers" use?