code: def delete_oldest(self):
          
          logger.info(
              "Deleting all mails sharing the oldest {} timestamp...".format(
                  self.oldest_timestamp))
          # Select candidates for deletion.
          candidates = [
              mail for mail in self.pool
              if mail.timestamp == self.oldest_timestamp]
          if len(candidates) == self.size:
              logger.warning(
                  "Skip deletion: all {} mails share the same timestamp."
                  "".format(self.size))
              return
          logger.info(
              "{} candidates found for deletion.".format(len(candidates)))
          for mail in candidates:
              self.delete(mail)
docs: Delete all the oldest duplicates.
  
          Keeps all mail of the duplicate set but those sharing the oldest
          timestamp.