why this email address is not allowed?

[luyuanx2]

[Andy Heinzer]

I think it's because this email address does not conform to the standards in https://en.wikipedia.org/wiki/Email_address

The domain name part of an email address has to conform to strict guidelines: it must match the requirements for a hostname, a list of dot-separated DNS labels, each label being limited to a length of 63 characters and consisting of:[6]:§2

• uppercase and lowercase Latin letters A to Z and a to z;
• digits 0 to 9, provided that top-level domain names are not all-numeric;
• hyphen -, provided that it is not the first or last character.

In your case, the domain is all-numeric, which likely is the reason that these addresses are invalidated.

[Yogesh Mude]

HI @luyuanx2

Welcome to the community!

You are adding numbers after @ sign please try to add like an example or any alphabets it will allow you.