UG (missing the last line have each domain label consist of alphanumeric characters, separated only by hyphens, if any):
App:
The local-part should only contain alphanumeric characters and these special characters, excluding the parentheses, (+_.-). The local-part may not start or end with any special characters.
This is followed by a '@' and then a domain name. The domain name is made up of domain labels separated by periods.
The domain name must:
end with a domain label at least 2 characters long
have each domain label start and end with alphanumeric characters
have each domain label consist of alphanumeric characters, separated only by hyphens, if any.
UG (missing the last line
have each domain label consist of alphanumeric characters, separated only by hyphens, if any
):App: