The on-line product "Stamps.Com" is immature technology. It is not ready to be accessed by the public and has restrictions on its use that are extream time and money wasters.
Please check out this product very carefully before you give them any money.
Their required on-line refund process does not work.
They require you to type in and reprint, on special labels you can only buy from them, an address on every piece on mail you want to put postage on.
All the pre-addressed envelopes you receive with your bills and every windowed envelope requires you to type in an address and have that address printed on an envelope or a lable that you then place over any pre-printed envelope!
And to top that off you can only use labels that you purchase from stamps.com.
This is a rip off and they are leading a lot of people down a path they are going to be very disapointed in the results of.