GAS(google app script)で指定ラベルのGmailをslackに通知

gistfile1.txt

var postUrl = "https://hooks.slack.com/services/xxxxxxxxxxxxxxxx";
var postChannel = "#chanel_name";
  
function myFunction() {
 
  // 未読の指定ラベル を検索
  var threads = GmailApp.search('is:unread label:to_me');
  
  var count = threads.length;
  Logger.log("対象件数:" + threads.length); 

  for(var i = 0; i < count; i++) {
      var lastDate = threads[i].getLastMessageDate();
      
      var datetime = lastDate.getFullYear() + "/" + (lastDate.getMonth() + 1) + "/" + lastDate.getDate()
      + " " + lastDate.getHours() + ":" + lastDate.getMinutes() + ":" + lastDate.getSeconds();

      Logger.log(datetime + " 件名：[" + threads[i].getFirstMessageSubject() + "]");
    　
    　//slackに通知
      sendHttpPost("件名:" + threads[i].getFirstMessageSubject() + " link:" + threads[i].getPermalink(), "GMAIL");
      
      //既読にする。
      //threads[i].markRead();
  }

}

function sendHttpPost(message, username)
{
  var jsonData =
  {
     "channel" : postChannel,
     "username" : username,
     "text" : message
  };
  var payload = JSON.stringify(jsonData);
  var options =
  {
    "method" : "post",
    "contentType" : "application/json",
    "payload" : payload
  };

  UrlFetchApp.fetch(postUrl, options);
}