That's how bulk shipping works. If you are a bulk mailer like, a cc company for example, then you would presort your mail to 5/9/11 digit and you get presorted discount from USPS even for first class mail.
So a postage stamp that costs you .50, costs a big mailer, may be, .40 depending on the sorting level and amount of mail.
So a postage stamp that costs you .50, costs a big mailer, may be, .40 depending on the sorting level and amount of mail.