What happens to unknown senders with the "Known Senders" filter on Mac or iOS?

If you've set the "Known Senders" filter for Mac text messages, what happens to messages from unknown senders? Do you get notified that they came, but they just aren't shown in your messages pane? That is, if I'm notified that they came in, I can always look at "Unknown Senders". But if I'm not given such notification, I won't even ever go look. I guess the same question applies to iOS.

[Re-Titled by Moderator]