Register airmail & ePacket
China post: http://www.17track.net/en

Arrival at transit office of exchange
Departure from outward office of exchange 


Sometimes, you will only get one of this tracking status. Both of them mean that your order 'left China and en route to destination country".
For orders to most countries, those status are the last ones. China post won't update it anymore.

Held by Customs 
Take it easy, it doesn't always mean that the customs seize your parcel. It also means that your parcel is processing in customs now, it will release sooner or later.


USPS
https://www.usps.com/
Status: Origin Post is Preparing Shipment
Here we point out that usually this status may not be updated till its final delivery.