Postal Letter - does anyone knows if usps has special rates for those who ship many packages every month ?

does anyone knows if usps has special rates for those who ship many packages every month ?

any other options to reduce shipping cost ?

Usually they have business rates (probably applies to high volume). Also try fedex or similar companies, they often have corporate rates.
If you are a business that ships a lot you can get an account with UPS and get a break on prices. I don't think that the US Postal Service has the same deal.
ya ask amazon .com and nike
Yes. but it has to be a very large shipments. contact your local post office and ask for Business Sales network. They can tell you more on how much the discounts are.