This is a very old conversation, but when I experienced the same problem mentioned here years later, I landed here, so I think that it is useful to write down here how I could solve/bypass the problem.
Apparently the Xiaomi server is unable to deal with grey listing. Hence, you don't get a response if your email service employs this ant-spam facility. Using a different email account without grey listing yielded an almost immediate response.
So, if you face the problem that you don't get an confirmation mail from Xiaomi, try to switch grey listing off (if you can) or use another email address for which grey listing is not configured.
After so many years of described error still the servers to Xiaomi doesn't work!
I have equipment that need to be register t use it and simple when I try to do it the reply is that user can't be create now, please try later
This is ridicules to a company which is pretending to be on the world market to block the users to use the equipment simple because - the servers are not running...