@IRonMaN  If you would paper file, you would not be using Stamps.com to get a delivery confirmation number.  That's because IRS has an unlisted address, at least for the Austin Service Center.  Stamps.com refuses to print labels or envelopes with the published IRS address because, they say, the Post Office does not recognize it as a valid address.  

The two government functions that Americans deal with most -- the Post Office and the IRS -- and they aren't talking to each other. 

(Same problem with Kansas City, but Ogden is accepted.)