I have recently been chided for not putting the full name on a parcel
to a person's home address. I have been told that without the family
name it will not be delivered!

I wrote Yukako Chan: Yukako being the given name and Chan being the
familiar suffix. 
The rest of the address was OK. ward, city country and included all
the right numbers in the right places: the subarea number, block
number and house number and the postcode.

From experience of the UK postal service I thought that the post
office would deliver the parcel to the correct address no matter what
the name of the recipient. The residents of the house would then
decide if the parcel was for someone they recognize. If it isn't they
can either open it anyway or write "return to sender".
I'm told instead that the post office look to see if the family name
is registered at this address and if it is not return it to sender
themselves or otherwise dispose of it. Consequently, addressing always
has to be done formally with the full name and the "joke name" that I
used will result in none delivery.

Does the Japanese postal system work in such a formal, complex way or
has my friend misunderstood the workings of the postal service?

-- 
Steve