I think the following code snippet should do what you’re requesting.
add_action('em_event_save', 'my_em_group_event_save', 10, 2);
function my_em_group_event_save($result, $EM_Event) {
if (is_object($EM_Event) && $EM_Event->group_id) {
$group = groups_get_group( array( 'group_id' => $EM_Event->group_id ) );
$post = get_post( $EM_Event->post_id );
$subject = sprintf( 'New post in %s: %s', $group->name, $post->post_title );
$message = sprintf( 'A new event has been added to the group "%s". To view the event, click the link below:%s%s', $group->name, "\n\n", get_permalink( $post_id ) );
$headers = array( 'Content-Type: text/html; charset=UTF-8' );
$recipient_list = array();
$members = groups_get_group_members( array( 'group_id' => $group_id ) );
foreach ( $members['members'] as $member ) {
$recipient_list[] = $member->user_email;
}
wp_mail( $recipient_list, $subject, $message, $headers );
}
return $result;
}
You can use the WPCode plugin to help you add the code snippet on your website.