Issue #3307736 by catch, alexpott: EmailValidator defaults to 'loose' mode...

   * {@inheritdoc}

   */

  public function validatedBy() {

    return '\Symfony\Component\Validator\Constraints\EmailValidator';

    return EmailValidator::class;

  }

}

<?php

namespace Drupal\Core\Validation\Plugin\Validation\Constraint;

use Symfony\Component\Validator\Constraints\Email;

use Symfony\Component\Validator\Constraints\EmailValidator as SymfonyEmailValidator;

/**

 * Email constraint.

 *

 * Overrides the symfony validator to use the HTML 5 setting.

 *

 * @internal Exists only to override the constructor to avoid a deprecation

 *   in Symfony 6, and will be removed in drupal:11.0.0.

 */

final class EmailValidator extends SymfonyEmailValidator {

  /**

   * {@inheritdoc}

   */

  public function __construct(string $defaultMode = Email::VALIDATION_MODE_HTML5) {

    parent::__construct($defaultMode);

  }

}