<prompt> Translate the following text to EnglishWakati barua barua monopoly ilitangulia kuanzishwa kwa huduma ya utoaji, gharama za kudumu zinazohusiana na utoaji ni msingi wa uthibitisho mbili za kisasa kwa ajili ya barua monopoly.  <response>: While the letter mail monopoly preceded the introduction of delivery service, the fixed costs associated with delivery underlie the two modern justifications for the letter monopoly. 