Ability to disallow confusing unicode characters to prevent homoglyph phishing attacks

When emails contain unicode characters that look similar to ascii characters, an attack vector is possible anytime we display the unicode email as an identifier of a user without punycode encoding the displayed email.

It would be nice to have an option to make confusing unicode characters fail email validation, but might be outside the scope of this library since it depends on the external confusables.txt data file from unicode.org?

The Unicode Consortium's Visual Spoofing Recommendations agree with this solution as a better alternative than blocking all unicode characters in domains and emails.

首先检查电子邮件验证的入口点，以及 issue 中引用的 Unicode TR39 confusables 数据。确定 opt-in 拒绝模式应如何使用 confusables.txt，并考虑在拒绝易混淆的 Unicode 字符而不阻止所有 Unicode 地址时所需的工作。