index.js

const request = require('request');

exports.postSlack = (req, res) => {
  let body = req.body;
  let message = makeMessage(body);
  //slackへの送信。環境変数にSLACK_WEBHOOK_URLを設定
  request.post({
    uri: process.env.SLACK_WEBHOOK_URL ,
    headers: {
      'Content-type': 'application/json',
    },
    json: {
      'text': message
    }
  });
 res.send(200);
};

//slackに送信するメッセージを作成
function  makeMessage(body){
  let event = body['event-data'].event;
  let storage = body['event-data'].storage;
  let message = body['event-data'].message;
  let recipient = body['event-data'].recipient;
  let title = '';
  if (event = 'failed'){
    title = 'メールの送信に失敗しました';
  }
  let messageText = message.headers.to + '：' + message.headers.subject;

  return [
    title ,
    'message：' + messageText,
    'URL：' + storage.url,
    '送信先：' + recipient 
  ].join('\n');
};