<prompt> Translate the following text to EnglishIkiwa mtoa barua mmoja alikuwa mkubwa wa kutosha kutoa wingi huo, au karibu kuutoa, mtoa barua huyo, kwa kutishia kuondoka Huduma ya Posta, anaweza kujadili viwango vya chini sana.  <response>: If one mailer were large enough to provide that mass, or nearly provide it, that mailer, by threatening to leave the Postal Service, might be able to negotiate extremely low rates. 