Do not, I repeat NOT place international parcels in the red box.

Yes, you can do it, and it even says as much on the eBay postage label. However, by doing so you won't have any proof of lodgement (either scan or receipt), and you risk not getting any tracking scans at all, because you'll be relying on other postal service companies to scan at their location.

If the tracking doesn't matter to you, and you have no issue with refunding the full purchase price plus postage, then by all means, save yourself a minute or two and bypass the AP scanner.

The time saved just isn't worth the monetary trade-off.