Email validation in Wordpress, Removed wp specific filter

/**
 * Verifies that an email is valid.
 *
 * Does not grok i18n domains. Not RFC compliant.
 *
 * @since 0.71
 *
 * @param string $email Email address to verify.
 * @param boolean $deprecated Deprecated.
 * @return string|bool Either false or the valid email address.
 */
function is_email( $email ) {


    // Test for the minimum length the email can be
    if ( strlen( $email ) < 3 ) {
        return false;
    }

    // Test for an @ character after the first position
    if ( strpos( $email, '@', 1 ) === false ) {
        return false;
    }

    // Split out the local and domain parts
    list( $local, $domain ) = explode( '@', $email, 2 );

    // LOCAL PART
    // Test for invalid characters
    if ( !preg_match( '/^[a-zA-Z0-9!#$%&\'*+\/=?^_`{|}~\.-]+$/', $local ) ) {
        return false;
    }

    // DOMAIN PART
    // Test for sequences of periods
    if ( preg_match( '/\.{2,}/', $domain ) ) {
        return false;
    }

    // Test for leading and trailing periods and whitespace
    if ( trim( $domain, " \t\n\r\0\x0B." ) !== $domain ) {
        return false;
    }

    // Split the domain into subs
    $subs = explode( '.', $domain );

    // Assume the domain will have at least two subs
    if ( 2 > count( $subs ) ) {
        return apply_filters( 'is_email', false, $email, 'domain_no_periods' );
    }

    // Loop through each sub
    foreach ( $subs as $sub ) {
        // Test for leading and trailing hyphens and whitespace
        if ( trim( $sub, " \t\n\r\0\x0B-" ) !== $sub ) {
            return false;
        }

        // Test for invalid characters
        if ( !preg_match('/^[a-z0-9-]+$/i', $sub ) ) {
            return false;
        }
    }

    // Congratulations your email made it!
    return $email;
}