Get webform submission data keyed by component's machine names instead of component's ids

gistfile1.php

<?php
 
/**
 * Implements hook_mail_alter().
 *
 * Add the wanted attachment to submission email.
 *
 * @param Array $message
 */
function MODULE_mail_alter(&$message) {
  if ($message['id'] == 'webform_submission' && $message['params']['node']->uuid == 'UUID OF YOUR WEBFORM') {
    $data = _tools_webform_get_submission_data($message['params']['submission'], $message['params']['node']);
 
    // Use $data here
  }
}
 
/**
 * Get webform components keys - cids relation
 *
 * @param stdClass $node
 *   The webform node
 *
 * @return Array
 *   form_key => cid
 */
function _tools_webform_get_components($node) {
  $cmps = array();
  if (!empty($node->webform)) {
    foreach ($node->webform['components'] as $cmp) {
      $cmps[$cmp['form_key']] = $cmp['cid'];
    }
  }
  return $cmps;
}
 
/**
 * Get an exploitable array of submission data indexed by components' form_key
 *
 * @param stdClass $submission
 *   The webform submission
 * @param stdClass $node
 *   The webform node [optionnal]
 *
 * @return Array
 *   form_key => mixed data
 */
function _tools_webform_get_submission_data($submission, $node = NULL) {
  if (NULL == $node) {
    $node = node_load($submission->nid);
  }
 
  $cmps = _tools_webform_get_components($node);
  $data = array();
 
  foreach ($cmps as $key => $cid) {
    if (!empty($submission->data[$cid])) {
      $data[$key] = $submission->data[$cid]['value'][0];
    } else {
      $data[$key] = '';
    }
  }
  return $data;
}