Why does spam go to the Known Senders group in Messages?

I've read many posts on this, here and on other forums — everyone says "just mark it as spam and block them". But that's never an answer to 'how are the spam messages able to get into my Known Senders group?'. Apple Support also routinely does not answer this question, e.g. , and my live support call from Apple had me go through the steps below + restart. I've routinely (monthly) restarted the phone, and this problem has been happening multiple times each week, for years. (i)Messages fully routes classical SMS at this point. If my settings are to *'only receive messages from those in my address book'* then how do any of these messages come through to the Known Senders list? 1. I have "filters unknown senders" turned on in my iOS settings. 1. The phone numbers or emails are clearly not from anyone that are in my known senders. 1. I've never received a message from them. 1. They've never been on a CC list with me. I'm fine if telecom protocols implicitly require that the message come to me — and that Apple auto-files it into a separate area (Unknown Senders) that I don't need to pay attention to. (I'm not actually but that's a longer rant +idea) But why does the spam keep coming into my main Known Senders feed of Messages?