Sarah Aubrey said:
The key is that you need to be reachable at that address.
That's it in a nutshell. And "reachable" does not mean that you have to live there or be instantly accessible to someone. As long as you retrieve your mail within a reasonable time, you'll be fine with everyone.
This question keeps coming up and a lot of bogus information has been given out as absolute gospel. Has anyone bothered to actually ask their post office about this? Well, I just did:
There is no USPS requirement to pick up your mail at any specified interval, though at least once a month is recommended if you receive an average amount of mail. If you use this as your "author's address" and you get almost no mail, you don't even need to check it that often.
You can tell your post office that you will only be in once a month or whenever so they will know ahead of time and not overstuff you box and not wonder if you died. That's not humor; they have special procedures that they have to do if you die, so, as long as they have reason to believe that you're still alive, all is good.
You are allowed to call the post office and have them check to see if you have any mail for pick up. Whether or not your particular post office will do that for you will depend on how good their customer service is. They are not required to do it, but mine will, for example.
You also have to make sure that the box rental fee is paid up. If your fee is not paid by the end of the month in which it is due, you have 10 days (or so) of grace period to get them the money. After that, your mail gets sent back.
The box rental fee depends upon the size of box that you rent and the zip code of your post office. As with almost anything else, when you buy in an upscale market, it costs more. The lowest fee for the smallest box in the most downscale market is $32.00 per year. I pay $68.00 per year for the smallest box in my post office. It also happens to be my actual place where I get mail, too. But it doesn't have to be...
You can be a resident of anywhere in the world and get a post office box in the United States, as long as the identification that you use to rent the box proves that you are the person that you say you are. They like your I.D to also have the physical address where you live, but that's not set in stone. There are people, for example, who live and travel around in an R.V. and have no permanent address. It's perfectly legal for them to have a P.O box somewhere, where they show up periodically to get their mail.
Finally, your P.O. box does not have to be the only place where you receive mail. You can have more than one P.O. box, as I do. You can also receive mail at a physical address as well as at a P.O. box. You can decide which address to use for which of your contacts. You are not "circumventing" any law by doing so, as long as you actually check periodically to see of you have any mail there.
I hope that all of this helps. And don't rely on rumors about what's "legal" and what isn't. The feds are not going to be tracking you down and pounding on your door because you use a special P.O. box to insulate yourself and your family from someone who might be a potential mental case. Especially nowadays, the Feds will probably have suggestions to help you do a better job of it.