Do the rules and procedures of the U.S. Postal Service ever confuse you? If so, the sources available on the Postal Explorer site might help to answer your questions. According to the site, "Postal Explorer is a virtual library of postal information and tools designed for U.S. Postal Service customers, business mailers, and employees. It puts a wealth of postal requirements for mailing and shipping domestically, internationally, and to APO/FPO/DPO destinations, at your fingertips in an easy-to-use format:"
If this site doesn't provide all the answers
you need, just send Uncle Sam a postcard to complain.