<prompt> Translate the following text to EnglishChini ya mikataba ya sasa Huduma ya Posta huweka bei kwa subclasses nzima na haiwezi kuchagua wateja maalum kwa ajili ya surcharges au punguzo.  <response>: Under current conventions the Postal Service sets prices for whole subclasses and cannot select specific customers for surcharges or discounts. 