You can send a long gun (rifle, shotgun) to another person
WITHIN YOUR STATE legally.
If you want to send a long gun to a person in another state I
believe it has to go through a FFL, but not sure if it has to
be an FFL on both ends.
You can only send a handgun USPS FFL to FFL.
All that said, if you order a CMP rifle it comes in the mail.