errormailcheck.js

function lineErrorWatch(){
  var token = PropertiesService.getScriptProperties().getProperty('SLACK_ACCESS_TOKEN');
  var slackApp = SlackApp.create(token);
  var channelId = "#xxx" // put your slack channel id here
  var slackId = "xxx"; // put your slack id here
  var boticon = "http://a274.phobos.apple.com/us/r30/Purple2/v4/72/47/a9/7247a999-3323-2063-e0d4-0cf48a8a2f82/mzl.nfffibwl.png"
  var start = 0;
  var max = 100;
  var filterString = 'label:line is:unread';
  var threads = GmailApp.search(filterString,start,max);
  var isToBreakOuterLoop = false;
  
  for(var i = 0; i < threads.length; i++) {
    var thread = threads[i];
    var msgs = thread.getMessages();
    //Logger.log(msgs.length);
    for(var j = 0; j < msgs.length; j++){
      var msg = msgs[j];
      if (!msg.isUnread()) continue;
      var body = msg.getBody();
      if (!body) continue;
      //Logger.log(body);
      var matches = body.match(/Error count\xa0\xa0<span style="color:#333333">([0-9]+)<\/span>/);
      var channelNameMatches = body.match(/Channel name\xa0\xa0<span style="color:#333333">(.*)<\/span>/);
      var channelName = "unknown";
      if (channelNameMatches && channelNameMatches.length >= 2) channelName = channelNameMatches[1];
      if (!matches || matches.length < 2) continue;
      var errorNum = parseInt(matches[1]);
      //Logger.log(errorNum);
      if (errorNum >= 5) {
        if (channelName.indexOf("テスト") != -1) {
          slackApp.postMessage("#dora_dev", "「" + channelName　+ "」から直近5分で最低" + errorNum + "つのエラーが確認されています", {username: "linebot" , icon_url: boticon});
        } else {
          slackApp.postMessage("#dora_dev", "「" + channelName　+ "」から直近5分で最低" + errorNum + "つのエラーが確認されています<@slackId>", {username: "linebot" , icon_url: boticon});
        }
        isToBreakOuterLoop = true;
        break;
      }
    }
    if(isToBreakOuterLoop) { break; }
    Utilities.sleep(1000);
   }
  threads.forEach(function(thread){ thread.markRead(); } );
}

http://qiita.com/soundTricker/items/43267609a870fc9c7453#botとして動かしてみる
ライブラリ使用