How does Apple filter short messages?

Taking the iphone 7 plus mobile phone as an example, the method of setting SMS filtering is as follows:

1. Find the setting icon on the desktop of the mobile phone system and click Open.

2. Then find the SMS option on the Settings page and click Enter.

3. Then find the option of filtering unknown senders on the current page, and click the switch button on the right to open this function.

4. Click the button to the right of the Filter Unknown Sender option, and the button will be in a green state, that is, the setting is successful.