get email addresses for a WordPress role.

qm_wp_roles.php

<?php
// get email addresses for a role.
// Usage: http://example.com/qm_wp_roles.php?role=author

require_once $_SERVER['DOCUMENT_ROOT'] . '/wp-load.php';
header( 'Content-type: text/plain' );
$input = empty( $_GET['role'] ) ? '' : strtolower( $_GET['role'] );
if ( empty( $input ) ) {
	echo qm_show_usage();
	exit;
} // end if missing role

if ( ! qm_valid_role( $input ) ) {
	echo qm_show_roles();
	exit;
} // end if invalid role

$results = qm_get_role_email( $input );
if ( empty( $results ) ) {
	echo "No users with role: {$input}\r\n";
} else {
	echo "To {$input}: {$results}\r\n";
} // end if no results.

exit; // The end.

function qm_show_usage() {
	return "Usage: http://{$_SERVER['HTTP_HOST']}{$_SERVER['REQUEST_URI']}?role=wp_role\r\n";
} // end qm_get_usage.

function qm_show_roles() {
	$lf    = "\r\n";
	$text  = "Valid Roles{$lf}";
	$roles = qm_get_roles();
	foreach ( $roles as $role ) {
		$text .= "{$role}{$lf}";
	} // end foreach

	return $text;
} // qm_show_roles

function qm_valid_role( $input ) {
	$roles = qm_get_roles();
	return in_array( $input, $roles );
} // end qm_valid_role

function qm_get_roles() {
	global $wp_roles;
	$data = array();
	foreach ( $wp_roles->roles as $key => $value ) {
		$data[] = $key;
	} // end foreach
	sort( $data );
	return $data;
} // end qm_get_roles

function qm_get_role_email( $input ) {
	$args       = array(
		'role'   => $input,
		'fields' => array( 'user_email' ),
	);
	$user_query = new WP_User_Query( $args );
	$j          = count( $user_query->results );
	if ( empty( $j ) ) {
		return '';
	} // end if no match.

	$got = '';
	for ( $i = 0; $i < $j; $i++ ) {
		$got .= $user_query->results[ $i ]->user_email . ',';
	} // end for
	return substr( $got, 0, -1 );
} // end qm_get_role_email