Anecdote: we use hosted Exchange from Microsoft. I tried to setup a cron job to email us all at 4:57 with the subject line "Get The Fuck Out". Those don't come through either.

And they don't respond to complaints, even from their own users.

I've been running the same pukka mailing list for 12 years, I'm in their abuse feedback loop, have proved exclusive ownership of the mail server, all mail is DKIM signed with valid SPF records, mail is accepted with a 250 OK, you name it.

Still they bin my emails, but only to some accounts. No rhyme or reason, no bounce, no spam folder. Just never arrives.

You could also reasonably configure a filter to not land emails over a spam threshold.

Given the amount and type of spam in my Gmail Spam label, I'm quite sure there's a hard filter in place there too.