<prompt> Translate the following text to EnglishMifumo kama hiyo inaweza kuruhusu viwango vya chini kwa barua zinazostahili, wakati vipande ambavyo havitastahili vinaweza kukataliwa au kuhitajika kulipa ada ya ziada kulingana na gharama.  <response>: Such systems might allow lower rates for qualifying mail, while pieces that would not qualify might be rejected or required to pay a surcharge based on costs. 