Shipping duty free goods home

Hello there, I am planning to travel to Japan in a few months and have a question regarding the duty free tax return. I read in your forum as well as in the article that a form (receipt?) will be attached to the passport for any duty free shopping made in Japan, and the custom officer will check and collect those form when I leave Japan.
My question is what if I am planning to mail these goods home through the post office in the airport? Is that possible because I don't think there are any post offices located inside once I go pass the customs. I am trying to save a bit on traveling by flying with LCC and am comparing whether it's cheaper to spend a bit more and up my luggage limit.
Thank you.

From my two times visit to japan, and from my experience, the customs at the airport only collected the receipts, and did not check for any items, further more, your tax are already deducted when you made the purchase, and the shops have already confirmed you are eligible for tax free.

I'm sure it's ok to leave japan through post, but whether customs will impose taxes in your country is another thing.

adding to my post, LCC flight need you to pay for luggage during your ticket booking, it's best to pay for more weight during your reservation usually 20KG/25KG or 30KG, anything extra above the 30KG will be charged at every 0.5KG at a set price, check with your airline company before reservation, remember that over weight limited during check in at the airport will cost more.

example of my luggage for HK Express are

20KG at HKD200 approximate USD26
25KG at HKD250 approximate USD32.25
30KG at HKD300 approximate USD38.70

some LCC airline allows you to have a carry on baggage upto 7KG in addition to no weight limit on duty free items, but not tax free items, these are two different things.