It appears that your splunk server is not allowed to relay via the smtp.sina.com.cn server. Splunk uses your $LOCALHOST variable to pass to the SMTP server. You might be able to adjust your hostname to be a fully qualified name, the SMTP server might accept it then. Alternatively you could also allow the Splunk server's IP to relay mail.
Any reason you can't just use the cnmail.systex.com.cn that already works to send your email?
Based on the error, its possible that updating the hostname in your alert_actions.conf file will resolve this. The mail is rejected due to "Partial domain not allowed: 'Jordan-PC'". What if you update your hostname to a fully qualified domain name?