Please sign the proof of delivery?

So every time I order from Zortrax (Poland) directly, immediately after shipping the package they send me a note saying:

/*

Dear Sirs,

 
Enclosed you will find the original invoice and proof of delivery for your last order. Please sign the proof of delivery and send a copy on e-mail address: <someone>@zortrax.com
 
 
Zortrax Accountancy Department
invoice@zortrax.com |
www.zortrax.com | www.zortrax.pl
 
<PDF Packing List>  <PDF Proof Of Delivery> <PDF VAT Invoice>
*/
 
I've replied to the email asking if/why I should sign the proof of delivery _before_ I've actually recieved the package, but get no response and eventually I get my package.
 
_IS_ there something I should be doing, or do I not understand something about this process?
 
Thanks!
 

I have not ordered anything from their website in a long time, but it sounds to me you are supposed to hold on to that email and after you get your products send back to them so they know you got it, that’s what it sounds like to me.

It has been sent by our Accountancy Department and its completely safe, there is nothing to be worried about. Sorry for any inconveniences.