How to retrieve the draft e-mails from google account and send it

 function draftMail() {  
  var threads = GmailApp.search('in:draft', 0, 10);  
  if (threads.length === 0) {  
   Browser.msgBox("No draft emails found");  
   return;  
  }  
  var myapp = UiApp.createApplication().setTitle('Select and Send Mail').setHeight(160).setWidth(300);  
  var top_panel = myapp.createFlowPanel();    
  top_panel.add(myapp.createLabel("Please select an email from your Drafts folder"));  
  var lb = myapp.createListBox(false).setWidth(250).setName('templates').addItem("Select draft...").setVisibleItemCount(1);  
  for (var i = 0; i < threads.length; i++) {  
   lb.addItem((i+1)+'- '+threads[i].getFirstMessageSubject().substr(0, 40));  
  }  
  top_panel.add(lb);  
  top_panel.add(myapp.createLabel("").setHeight(10));  
  top_panel.add(myapp.createLabel("").setHeight(5));  
  var ok_btn = myapp.createButton("Send Email");   
  top_panel.add(ok_btn);  
  myapp.add(top_panel);  
  var handler = myapp.createServerClickHandler('sendMail').addCallbackElement(lb);  
  ok_btn.addClickHandler(handler);  
  SpreadsheetApp.getActiveSpreadsheet().show(myapp);  
 }  
 function sendMail(e) {  
  try {  
   var ss = SpreadsheetApp.getActiveSpreadsheet();  
   ss.toast("I'm sending the email, please wait...",'Gmail',-1);   
   var draft = GmailApp.search("in:drafts")[(parseInt(e.parameter.templates.substr(0, 2))-1)].getMessages()[0];  
   var body = draft.getPlainBody();  
   var to = draft.getTo();  
   var subject = draft.getSubject();  
   GmailApp.sendEmail(to, subject, body);   
   ss.toast('Your email is sent to ' + to);   
  } catch (e) {  
   ss.toast(e.toString());  
  }  
  var app = UiApp.getActiveApplication();  
  app.close();  
  return app;  
 }