How does postal mail get sorted?

I know how it gets sent either by truck or plane, but how does it get sorted? Do they sort by State, then city, then zip code or what? How does it work?How does postal mail get sorted?
In the early years mail was sorted by hand so each piece of mail was touched by someone many times. Now mail is sorted by machine that optically scans the written numbers and letters and sorts them mechanically. There are also bar codes that are placed on letters that are easier to scan and route to the appropriate addressee,



About the only time it麓s touched now is when it麓s delivered to your home or business by the friendly mail person.How does postal mail get sorted?
Well they scan it and send it by zip code zones - however if it has Anthrax it is sent to Dick Cheney and he forwards it on to Sen. Tom Daschle