A Google Apps Script for trashing aged mails.

MailTrasher.gs

// Set this function as Trigger
function myFunction() {
  const queries = [
    "from: to-be-trashed@hoge.fuga.com",
    "from: high-frequently-ads@hoge.fuga.com"
  ];
  trashMails(queries);
}

function getDateBefore7Days() {
  var date = new Date();
  date.setDate(date.getDate() - 7);
  return date;
}

function trashMails(queries) {
  const fromDate = getDateBefore7Days();
  const year = fromDate.getFullYear();
  const month = fromDate.getMonth();
  const date = fromDate.getDate();
  const fromDateString = year + "/" + (month + 1) + "/" + date;
  
  var isFirstDelete = true;
  
  queries.forEach((query) => {
    const searchQuery = query + " is:all NOT is:trash before:" + fromDateString;
    const threads = GmailApp.search(searchQuery);

    Logger.log(searchQuery);
    if (threads.length == 0) {
      Logger.log("No results.");
      return
    } else {
      Logger.log(threads.length + " results.");
    }
  
    var titles = "";

    if (isFirstDelete) {
      titles = "*DELETE MAILS BEFORE " + fromDateString + "*\n";
      isFirstDelete = false;
    }

    titles += "*" + query + "*\n";
  
    threads.forEach((thread) => {
      titles += "- " + thread.getFirstMessageSubject() + "\n"
    })
    
    // POST to Slack
    const postUrl = "https://hooks.slack.com/services/***hogehogehogehoge***";
    const jsonData = {
      "username": "Mail Trasher",
      "icon_emoji": ":wastebasket:",
      "text": titles
    };
    const payload = JSON.stringify(jsonData);

    var options = {
      "method" : "post",
      "contentType" : "application/json",
      "payload" : payload
    };

    var response = UrlFetchApp.fetch(postUrl, options);

    // move to Trash if responseCode is 200
    if (response.getResponseCode() == 200) {
      threads.forEach((thread) => {
        thread.moveToTrash();
      });
    } else {
      Logger.log("Slack unexpected response code: " + response.getResponseCode());
      Logger.log(response.getAllHeaders());
      Logger.log(response.getContentText());
    }
  }); 
}