Create a normalized version of an email address containing UTF8 characters in the domain part according to IDNA2008.

IdnEmailExample.java

package org.example;

// https://mvnrepository.com/artifact/com.ibm.icu/icu4j/73.1
import com.ibm.icu.text.IDNA;
// https://mvnrepository.com/artifact/com.sanctionco.jmail/jmail/1.5.0
import com.sanctionco.jmail.Email;
import com.sanctionco.jmail.EmailValidationResult;
import com.sanctionco.jmail.JMail;

public class IdnEmailExample {

    private static final IDNA validator = IDNA.getUTS46Instance(
            IDNA.NONTRANSITIONAL_TO_ASCII
                    | IDNA.NONTRANSITIONAL_TO_UNICODE
                    | IDNA.CHECK_BIDI
                    | IDNA.CHECK_CONTEXTJ
                    | IDNA.CHECK_CONTEXTO
                    | IDNA.USE_STD3_RULES);

    public static void main(String[] args) {

        String address = toAscii("you@déjà.VU.straße.example.com");
        // Returns: you@xn--dj-kia8a.vu.xn--strae-oqa.example.com

        if (null == address) {
            System.out.println("Invalid email address.");
        } else {
            System.out.println("Ascii email address: " + address);
        }
    }

    /**
     * Returns a normalized version of an email address containing
     * UTF8 characters in the domain part according to IDNA2008.
     */
    public static String toAscii(String email) {

        EmailValidationResult result = JMail.validator().validate(email);

        if (result.isFailure()) {
            System.out.println("Failure: " + result.getFailureReason());
            return null;
        }

        Email parsedEmail = result.getEmail().get();

        if (parsedEmail.isIpAddress()) {
            return parsedEmail.normalized();
        }

        IDNA.Info info = new IDNA.Info();
        StringBuilder asciiDomain = new StringBuilder();

        validator.nameToASCII(parsedEmail.domainWithoutComments(), asciiDomain, info);

        if (info.hasErrors()) {
            System.out.println("Errors: " + info.getErrors());
            return null;
        }

        return parsedEmail.localPartWithoutComments() + "@" + asciiDomain;
    }

}