first check with the local post office about mail preparation and costs and see whether it is making sense for your business.
if you mail a lot of items using priority mail, it is a good idea to use envelopes and boxes that are provided by the post office.
you should be keeping your eyes on the weight. if the weight of the envelope or box you are getting from the post office bumps the package to the next weight category, then you might be forced to pay more than what you would have if you bought your own boxes and choose to ship it priority mail.
many of the major shipping provider 