I have set up SPF with DMARC as well as DKIM. I have never sent suspicious emails. I even add OpenPGP signing to my emails. SpamAssassin and GMail filters seem to not have any problems, when I check it with external tools. Yet still, my emails keep landing in spam folders of people unless they specifically add me to their contacts.
What could be the reason? Do email clients/servers not like email from custom domains? Or is it just because my email server is in Russia? 🙄
Alright, I've been advised (thx @kev and @0xedd1e)and to set up a PTR record for reverse DNS. Folks who use custom domain e-mails managed by others (Gmail, Mailbox.org, etc.): How do you do that? Do you contact the company? Do they do that automatically for you?