iCloud Mail will silently filter emails with certain words (including in attachments).

You aren’t told something has been filtered and it doesn’t go to spam. It’s just deleted with zero recourse. The sender isn’t notified either.

https://talk.macpowerusers.com/t/icloud-mail-what-to-do-when...

I had this happen as recently as June 2026 when my current provider was up. It happens on @mac.com @me.com @icloud.com and custom domains.