He said that the parcel had been returned to him "addressee unknown". We checked the address and it was all correct, so I'm not sure what happened.
This has happened to me too, not with Parkers but when I sent something to Germany. Deutsch Post apparently tried delivery
twice to the address.
When the package was returned to me, I could see 2 failed delivery address notices on it... despite the address being perfect! I tried to get compensation but La Poste said it was not their fault and shrugged (you get lots of shrugging in France!). I re-sent the package, same address and all was fine... except me being out €25!
I can only assume postman number 1 couldn't find it, and so they didn't bother even looking the 2nd time and just stuck the 'address unknown' sticker on it again.