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although in these days of heightened awareness of sexist language,
the term mail carrier is preferred.
Stamps are sold at post offices and from vending machines and
can sometimes be bought in supermarkets and drugstores.

SENDING AND RECEIVING LETTERS AND
PACKAGES

The post office wants people to put their own address, called
the return address, on the upper-left-hand corner of an envelope or
package, rather than inside on the letter itself. If for some reason
your letter or package cannot be delivered, it will be returned to
you if your address is on the outside.
Addresses in the United States use a two-letter abbreviation of
the state and a ZIP code after the state. The ZIP code is a five- digit
number that helps a local post office find your address more
accurately. In 1983, an additional four-digit code was added to ZIP
codes that included further delivery information but most people
continue to use just the five-digit number.
Letters can be put in blue mailboxes found on city streets, or
they can be put in a home's own mailbox where mail is delivered.
The mail carrier will pick them up when delivering the day's mail.
Private mailboxes often have a little red flag that can be raised to
show that mail is waiting to be picked up.
Mailboxes are usually found by the sidewalk at the edge of a
house's property, rather than mail being dropped through a slot in
the door. Some houses, especially in cities, have a metal box
attached to the house near the front door. In apartment buildings,
mail will be put in individual boxes just inside the door; mail
carriers do not usually pick up outgoing mail from apartment
buildings.
Packages that weigh more than one pound have to be taken to
the post office to be mailed. Packages are cheaper to send than
letters as long as you don't put a letter inside the package; if you
do, and you are silly enough to tell them you have, you will be
charged the full letter rate for the weight of the package.