docs: def save_email(self, list_name, email_msg, index):
          """Save email message into the database."""
  
          msg_id = email_msg.get('Message-ID')
          if not msg_id:
              return
  
          # Update last imported message into the DB
          mailinglist, created = MailingList.objects.get_or_create(
              name=list_name
          )
          mailinglist.last_imported_index = index
  
          if created:
              # if the mailinglist is newly created it's sure that the message
              #   is not in the DB yet.
              self.create_email(mailinglist, email_msg)
  
          else:
              # If the message is already at the database don't do anything
              try:
                  Message.all_objects.get(
                      message_id=msg_id,
                      thread__mailinglist=mailinglist
                  )
  
              except Message.DoesNotExist:
                  self.create_email(mailinglist, email_msg)
  
          mailinglist.save()