input: Write a function that takes a list of email addresses as input, iterates over the list, and sends an automated email to each address. The function should use the SMTP protocol to send the emails. If the emails are sent successfully, the function should print 'Email sent successfully.' for each email sent.
  
  assert send_automated_email(["email1@example.com","email2@example.com"])==None
  assert send_automated_email(["email3@example.com"])==None
output: def send_automated_email(email_list):
      import smtplib
      from email.mime.text import MIMEText
      from email.mime.multipart import MIMEMultipart
  
      sender_email = "your_email@example.com"
      sender_password = "your_password"
  
      for email in email_list:
          message = MIMEMultipart()
          message["From"] = sender_email
          message["To"] = email
          message["Subject"] = "Automated Email"
          body = "This is an automated email."
          message.attach(MIMEText(body, "plain"))
  
          with smtplib.SMTP("smtp.example.com", 587) as server:
              server.starttls()
              server.login(sender_email, sender_password)
              server.sendmail(sender_email, email, message.as_string())
              print('Email sent successfully.')