Osaka International Post Office

If you googled this place wondering where to give back your Pocket WiFi (like I did), you don't need to go so far: there is a post box at the entrance of Terminal 1 as you leave the hall of the JR Haruka station.

XOXO

風景印配備局。

関空駅前から、貨物地区行きのバスに乗る必要があります。保安上、徒歩では行けません。

バスに乗るにはゲートがあり、許可証が必要。警備所で手続き、要公的機関身分証。

局にて訪問印をもらい、許可証は帰りに返却。

海外からの国際郵便がこちらで１週間追跡が動かないので、連絡しました。
女性の方が出られましたが口調も丁寧で色々と調べていただいて解決しました。

Troche opóźniona, ale pocztówka dotarła do Polski

風景印の記念押印に快く応じていただけた。
訪問するには関空バス停で関西エアポートの許可証（無料）を発行してもらい有料のバスで行かねばならない。一般客は徒歩での往復は不可能。必ずバスで往復する必要があります。

Terrible service. I paid for an express delivery through EMS. They could not get my very small documents package on a flight, therefore it sat at KIA for 10 days - I did not hear anything, I just kept checking my tracking information and I had to call EMS multiple times to find out what was happening.
They then cancelled my shipment (with no contact) I had to call EMS again as it was 'returned to sender' only I still have not received my parcel four days after the fact.
None of this experience was express and they do not even seem to care that I have stated how important these documents are or why I need them sent or received back so quickly.

I would recommend paying extra and using a service like DHL or FedEx.

Extra: I called EMS again today and got a very helpful customer service assistant and they called the airport for me and my parcel was returned to me in a few hours with forms for a refund. So helpful, thank you EMS!!