If asked by a postal employee if it is a firearm the correct answer is yes. Don't be a dumbass. They are entitled to inspect it to assure it meets the regulations, long gun, unloaded, no ammo.
Can he mail it without being there? I don't know. Interesting question. Pre-labled with his info and you are just dropping it off? I'd do it.
The correct answer is none of your fugging biz.They cannot open to check out what it is.They will ask if it is" liquid,flammable or batteries."Also you do not need to lie about what it is because if it is not one of the things they mentioned,you don`t have to tell them.