Weren't you trying to get your FFL01? You'd think you would know the law!It's illegal unless your sending it to an FFL.
Since the lower receiver can be used in the construction of a Handgun, it will have the same restrictions as any handgun, therefore cannot be shipped to an individual. It must be shipped to an FFL holder.
You can ship in state to another Indiana resident who is not a prohibited person. Usps is fine for non handguns. Fedex or Ups for handguns. This comes up pretty often. Look at the ATF FAQ's it's on there.
Google ATF FAQ. It's numbers 7 and 8