I am using Apple Mail for a single mac.com email account. I am getting Sucuri security notifications from a WordPress website that I worked on 5 or so years ago. They go directly to the Apple Junk folder. I’ve tried using Rules in Apple Mail, adding the sending email to Spam Sieve Blocklist but nothing has any effect on theses emails. I get at least 50 of these things a day.
That’s normal because the iCloud server junk filter is catching them before they get to your Mac. SpamSieve does not process spam messages that were already caught, so it is not missing them, and you should not train them as spam.