WEIRD POSTAL CODES

I'm metering letters today at work that are going to places I didn't think were considered "domestic" mail. You know how all the states have those two letter codes (i.e., North Carolina = NC)? Well, I came across PW and FM today.... So apparently these places are part of the US.... I knew that Puerto Rico (PR) and the US Virgin Islands (VI) were considered domestic destinations for the US Postal Service, but there are a few I have never seen before. How many do you recognize?: FM, MH, MP, PW. After looking these up at the postal service web site, I still don't know where any of them are....