Google Apps Script to accompany "email to task mechanism" post https://qmacro.org/2011/10/04/automated-email-to-task-mechanism-with-google-apps-script/

taskscript.js

// -----------------------------------------------------
// Globals, contants
// -----------------------------------------------------
TASKLIST = "DJ's list";
LABEL_PENDING = "newtask";
LABEL_DONE = "newtaskdone";

// -----------------------------------------------------
// getTasklistId_(tasklistName)
// Returns the id of the tasklist specified
// Oddly, we should be able to use:
// Tasks.Tasklists.get(tasklistName)
// but it always gives an error "Invalid Value".
// -----------------------------------------------------
function getTasklistId_(tasklistName) {
  var tasklistsList = Tasks.Tasklists.list();
  var taskLists = tasklistsList.getItems();
  for (tl in taskLists) {
    var title = taskLists[tl].getTitle();
    if (title == tasklistName) {
      return taskLists[tl].getId();
    }
  }
}

// -----------------------------------------------------
// processPending(sheet)
// Process any pending emails and then move them to done
// -----------------------------------------------------
function processPending_(sheet) {

  var label_pending = GmailApp.getUserLabelByName(LABEL_PENDING);
  var label_done = GmailApp.getUserLabelByName(LABEL_DONE);

  // The threads currently assigned to the 'pending' label
  var threads = label_pending.getThreads();

  // Process each one in turn, assuming there's only a single
  // message in each thread
  for (var t in threads) {
    var thread = threads[t];

    // Grab the task data
    var taskTitle = thread.getFirstMessageSubject();

    // Insert the task
    addTask_(taskTitle, TASKLIST);

    // Set to 'done' by exchanging labels
    thread.removeLabel(label_pending);
    thread.addLabel(label_done);
  }

  // Increment the processed tasks count
  var processedRange = sheet.getRange("B1");
  processedRange.setValue(processedRange.getValue() + threads.length)
}

// -----------------------------------------------------
// addTask_(title, taskListId)
// Create new task and insert into given tasklist
// -----------------------------------------------------
function addTask_(title, tasklistId) {
  var newTask = Tasks.newTask().setTitle(title);
  Tasks.Tasks.insert(newTask, getTasklistId_(tasklistId));
}

// -----------------------------------------------------
// main()
// Starter function; to be scheduled regularly
// -----------------------------------------------------
function main_taskconverter() {

  // Get the active spreadsheet and make sure the first
  // sheet is the active one
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sh = ss.setActiveSheet(ss.getSheets()[0]);

  // Process the pending task emails
  processPending_(sh);

}