Why do mobile phones receive yellow spam messages?

Apple's mobile phone can open the notification of filtering unknown senders and blocking non-mobile phone contacts after receiving yellow spam messages, and open the filtering of unknown senders through the following steps:

Apple's mobile phone receives yellow spam messages

1. Open the phone settings and click? Information? Enter the information setting page.

2. click? Filter unknown senders? You can stop yellow spam.

operating environment

Brand model: iPhone 13

System version: ios 15. 1. 1.