Why does the QQ number appear in the message received by the other party when Apple sends a message?

That's because you used the iMessage function. Apple and Apple directly have a function called iMessage. This function allows Apple and Apple to send text messages directly for free, so the account number of QQ mailbox is displayed. Apple and other brands of mobile phones do not have this function, so the mobile phone number is displayed.

IMessage is a cross-device network short message service provided by Apple for iOS 5. It allows devices such as iPad and iPod Touch that are not bound with mobile phone numbers to communicate with iPhone instantly, and can send text, pictures and videos, which is basically the functional experience of SMS.

As long as the iOS device is upgraded to iOS 5 and can access the Internet, you can send and receive SMS for free and unlimited through iMessage. The security of IMessage is very high.

To display the other party's mobile phone number, just go to Settings-Info-Turn off iMessage.