Post box

I try to find post box to send mail easier than to go to post office... But I didn't found it...

Finally, I know that the United States doesn't have post box but it uses another way to send mail, maybe it looks more comfortable; in front of any house has post box, then if someone in house who wanna send a mail, already including a stamp, can put it in that post box and raise a red flag up to tell a postman that there are sth to send. When a postman come to send a mail, he will know and pick it up by himself... Ohh! Surprise!