code: def delete_older(self):
          
          logger.info(
              "Deleting all mails strictly older than the {} timestamp..."
              "".format(self.newest_timestamp))
          # Select candidates for deletion.
          candidates = [
              mail for mail in self.pool
              if mail.timestamp < self.newest_timestamp]
          if len(candidates) == self.size:
              logger.warning(
                  "Skip deletion: all {} mails share the same timestamp."
                  "".format(self.size))
          logger.info(
              "{} candidates found for deletion.".format(len(candidates)))
          for mail in candidates:
              self.delete(mail)
docs: Delete all older duplicates.
  
          Only keeps the subset sharing the most recent timestamp.