Check your local library. Vance Tremble is the author, "Overnight Success, The Story of Federal Express's Renegade Founder-Frederick Smith"
Tremble does admit that Mr. Smith has never and probably will never be interviewed for a Biography, he is just not interested. However, there was some heavy duty research and interviews of other FedEx Execs and Smith family members done for this book that gives great background on the entire evolution of FedEx. It's an easy and enjoyable read.