I don't think that is what you are looking for. eShipping is a freight forwarder, a freight consolidator and a contract fullfillment operation.
If you plan on shipping 5000 flags to a single destination, then you're in the right place, but you'll probably do better going straight to a common carier youself.
If the post office can't handle your requirements or it's too expensive, checkout CanPar and UPS freight services. Shipping via common carrier is a very competitive business, shop around.