The visible elf/ how the owls do it?

[spang_b]

No: HPFGUIDX 87789

Hi, I have a couple of questions.
   In OOTP, the headquarters of Order of Phoenix is supposed to be 
unplottable and under fidelius charm or something. Then how come 
Harry's owl Hedwig finds it when he sends letters? Come to think of it, how 
do owls find Hogwarts when it is supposed to be unplottable? And how 
come they always find their targets without addresses? Couldn't 
someone  like Voldemort just  send an owl and track it trusting that 
it would always find its target?

Also in OOTP, in the first chapter, after the mysterious crack of 
diapparating Mundungus, Harry is sure that it is not Dobby. The line 
goes something like Harry is sure that the house-elf cannot be 
invisible. Why can't the house-elves be invisible?


spangb