Certified mail and another $7 will get you a cup of coffee at Starbucks.  It does not receive special handling by the Post Office.  It does not receive special handling at IRS and often the "return receipt" card is not sent back.  It doesn't prove that a return was sent to IRS, but it does provide some evidence when there is a question of whether a filing deadline was met.  For responding to an IRS notice, though, it is simply stupid.  If anything it delays the response if scanning takes another day or two.