I got his email too.
There are several ways to consider this.
If he was scamming us all, why bother with this email? It ties him into the deal even more doesn't it. And it updates his involvement to the present, rather than several weeks ago.
Assuming it's legit, the boards should start arriving sometime, but who knows when. If nobody gets their board in say one, two or three weeks time, they are either all stuck in the same place somewhere, or we have indeed been scammed. In that case, we should get the cops involved. The question is how long do we give it now?
As to the value of the receipt. It's an official document issued by the German Postal Service and that must carry a lot of weight.
With a receipt of posting, you can indeed get a search done. I've gone through this before with the Royal Mail. Someone posted me a parcel from Venezuela which got 'lost'.
I believed there was probably no chance of my ever seeing it, espacially from South America.
Anyway, I sent a copy or the proof of posting and a few weeks later, the Royal Mail came up trumps. It had been 'held up' by customs people in South America. Anyway, after that the Royal Mail is great as far as I'm concerned!
Cheers,
JaX