From the ATF:
(B1) To whom may an unlicensed person transfer firearms under the GCA?
A person may sell a firearm to an unlicensed resident of his or her state, if the buyer is not prohibited by law from receiving or possessing a firearm, or to a licensee in any state. A firearm other than a curio or relic may not be transferred interstate to a licensed collector. [18 U. S. C 922( a)( 3) and (5), 922( b)( 3), 27 CFR 178.29]
AND
(B8) May a nonlicensee ship a firearm through the U. S. Postal Service?
A nonlicensee may mail a shotgun or rifle to a resident of his or her own state or to a licensee in any state. Handguns are not mailable. A common or contract carrier must be used to ship a handgun. A nonlicensee may not transfer any firearm to a nonlicensed resident of another state. The Postal Service recommends that longguns be sent by registered mail and that no marking of any kind which would indicate the nature of the contents be placed on the outside of any parcel containing firearms.
From: http://www.atf.gov/firearms/faq/faq2.htm#b1
Interstate = FFL needed on receiving end
Intrastate – No FFL needed, same as a FTF transfer, unless your state requires something different (I live in FL).
Here are the basic guidelines I use when I have sold firearms this way: I request a signed statement that the buyer is over 18 and is legally able to purchase and posses a firearm and that they cannot hold me responsible for how it is used, etc. I do not ask for a copy of an ID since I do not have a face to put it to (make sure it is theirs) – I my opinion it is meaningless. I also only take USPS money order for payment and ship UPS adult signature. I think that if your state allows it and you follow guidelines similar to those above you will be ok.