I am avoiding all postal jokes that I can... but this is oh so tempting.
I do not know the answer to the question, but the sites the other people provided look good to me.
Also, - this is very important-
PLEASE MAKE SURE THE DAMNABLE STAMP VENDING MACHINE ALWAYS HAS STAMPS/CHANGE in it - it seems everytime I go to a frickin' post office the machine is not working/needs stamps/needs coin - then guess what - 15 minutes on a line to get a frikin' book of stamps.
*rant off.
Thank you.
Good luck on your test !