http://about.usps.com/who-we-are/postal-facts/one-day-by-the-numbers.htm
This is just one day's numbers. No wonder domestic is so safe for the most part.
Edit: For those who don't want to get off TOR to view:
Just one day in the life of the U.S. Postal Service... by the numbers
Each day the Postal Service picks up, processes and delivers millions of letters and packages. No single operation in the world comes close to this level of connectivity to so many households and businesses. Here's just ONE day in the life of the United States Postal Service. (Figures are averages.)
227.1 million -- revenue received, in dollars
5.9 million -- dollars paid to postal employees in salaries and benefits
509 million -- number of mailpieces processed and delivered each day
21.2 million -- average number of mailpieces processed each hour
353,000-- average number of mailpieces processed each minute
5,890 -- average number of mailpieces processed each second
206 million -- pieces of First-Class Mail processed and delivered
7,184 -- number of letter carriers who deliver mail entirely on foot -- The USPS Fleet of Feet
122,000 -- number of address changes processed
3,630 -- number of addresses added to our delivery network
4.1 million -- number of people who visit usps.com
758,356 -- dollar amount of online stamp and retail sales at usps.com
1.5 million -- amount of money spent on postage for Click-N-Ship labels
146,850-- number of Click-N-Ship labels printed
306,930 -- number of money orders issued
1.5 million -- dollars spent at self-service kiosks in Post Office lobbies
0 -- tax dollars received for operating the Postal Service
21 million fucking parcels!!!!!!!!!!! Props to the mailman and the crew, they're doing god's work