Niu email format
You're referring to the email format used by Niu, a Chinese online education platform!
The Niu email format is typically in the following format:
Where username is a unique identifier chosen by the user during registration.
For example:
Note that the @niu.com part is fixed, and the username part can be any combination of letters, numbers, and special characters (except for spaces and certain special characters that are not allowed in email addresses).
I hope that helps!