As far as I can determine (although, I may be missing something), once
confidential and anonymous email is supported, removing that support
will be very hard.
With tools like RIPEM and PGP (and even TISPEM, which allows for
unsigned encrypted messages), plus anonymous remailers like the one
run by Julf Helsingus in Finland, we are already (almost) at this
point.
I will also point out that either of your scenarios could (and
probably already have been) carried out using "snail mail". The post
office does not verify the authenticity of return addresses, and it is
fairly simple to avoid the usual traps (fingerprints, DNA matching
from saliva on the envelope glue, obvious handwriting..) and quietly
drop the letters into a mailbox in the middle of the night when nobody
is watching.
- Bill