Send emails with text from a textbox called from crontab

emailSender.py

#!/usr/bin/python
# -*- coding: utf-8 -*-

import os
from Tkinter import *
import tkMessageBox
import smtplib
import sys
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText
from email.header import Header

def Call():

  global root
  sender = 'Nome 1 <email1@exemplo.com>'
  receivers = ['Nome 2 <email2@exemplo.com>', 'Nome 3 <email3@exemplo.com>', 'Nome 4 <email4@exemplo.com>']

  msg = MIMEMultipart('alternative')
  msg['Subject'] = Header("Envio de relatório diário", 'utf-8')
  msg['From'] = sender
  msg['To'] = ", ".join(receivers)
  
  text = "A actividade de hoje foi:\n\n\n\n" + tb.get("1.0",'end-1c')

  msg.attach(MIMEText(text.encode('utf-8'), 'plain', 'utf-8'))


  try:
    smtpObj = smtplib.SMTP('smtp.office365.com',587)
    smtpObj.ehlo()
    smtpObj.starttls()
    smtpObj.ehlo()
    smtpObj.login('emailAqui','passwordAqui')
    smtpObj.sendmail(sender, receivers, msg.as_string())
    smtpObj.quit()
    tkMessageBox.showinfo("Sucesso", "A sua mensagem foi enviada com sucesso.")
    root.quit()
  except SMTPException:
    tkMessageBox.showinfo("Erro", "Ocorreu um erro a enviar a mensagem")

os.environ["DISPLAY"] = ":0.0"
root = Tk()
root.wm_title("Report sender")
root.geometry('600x675')
tb = Text(root, height = 40)
tb.pack(side=TOP,pady=10)
button = Button(root, text = 'Send report!', command = Call)
button.pack(side=TOP,pady=10)

root.mainloop()
root.destroy()