Veritaserum/Owls

[finwitch at yahoo.com]

No: HPFGUIDX 29974

Well, there is restrictions on the use of Veritaserum:

It may only be used by agreement of the person, simply to avoid 
Veritaserum causing a Secret-Keeper to tell the Secret!

Possibly it's also banned on Minors (3 drops and you tell 
everything? - if a child of 5 would have that... the child might die 
or never be able to lie or keep a secret).

And on Owls:

Owl can't be magically tracked, but can be noticed and followed - or 
even killed.

An owl will deliver all letters, unless it's tired etc. They fly - 
much like ordinary owls, not apparate or otherwise magically 
transport themselves. Within it's abilities, an owl will try to 
deliver the letter...

About to whether an owl can be blocked...
I think not. Harry's not getting any Owl-fanmail, because his fans are
a) adults who know better than to send such letters to children
b) Children who might send such but don't have owls and do have 
parents telling them not to.