How to make people unable to send black messages?

How to hack messages that people can't send is as follows (take iPhone as an example):

1. Open the settings application.

2. Scroll the screen and select the Info option.

3. On the Information page, select the Unknown and Filtered Information option.

4. Turn on the "Filter Unknown Sender" switch.

5. Return to the information page and select the "Blocked Contacts" option.

6. Click the Add New Contact button.

7. On the Add Contact page, enter the phone number or contact name to block.

8. Select the contact you want to block, and then click the Finish button.