There is a bunch of misinformation here in my opinion. Anyone can mail a long gun across state lines as long as it goes to an FFL in the receiving state. This is through the USPS. Handguns cannot be mailed except by FFLs. A P320 frame, without the serialized Fire Control Unit, can be mailed or shipped via UPS or FedEx. Those parts are not firearms.
Here is a blurb from the ATF website:
A nonlicensee may not transfer a firearm to a non-licensed resident of another state. A nonlicensee may mail a shotgun or rifle to a resident of their own state or to a licensee in any state.
The U.S. Postal Service recommends that long guns 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.
Handguns are not mailable. A common or contract carrier must be used to ship a handgun.
[18 U.S.C. 1715, 922(a)(5) and 922 (a)(2)(A); 27 CFR 478.31]
Here is a blurb from the ATF website:
May a nonlicensee ship a firearm through the U.S. Postal Service?
A nonlicensee may not transfer a firearm to a non-licensed resident of another state. A nonlicensee may mail a shotgun or rifle to a resident of their own state or to a licensee in any state.
The U.S. Postal Service recommends that long guns 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.
Handguns are not mailable. A common or contract carrier must be used to ship a handgun.
[18 U.S.C. 1715, 922(a)(5) and 922 (a)(2)(A); 27 CFR 478.31]