QQ mailbox cannot add 126 mailbox.

You need to log in to 126 mailbox and open this POP3/SMTP service. You need to use your mobile phone to scan the code and send text messages. Just follow the prompts.

Then add an authorization code, you need to scan the code with your mobile phone and send a text message. Please also follow the prompts.

Restart the phone, open the QQ mailbox, add the 126 mailbox, and fill in the authorization code in the password position. Then it was set successfully. You can also open the webpage version of QQ mailbox, add 126 mailbox in other folders, and use the authorization code for the password. The authorization code is displayed only once, which is relatively long. You can copy, paste and save.

I've tried both. You can try.