I will reply properly when I am back at my keyboard this weekend. Just
one thing now: the two extensions are subtly but crucially
incompatible.
Nothing in 653x requires a receiver to support idna (or
a-label encoding of local parts), or to treat them the same way as
u-labels. The sender has to chose encoding without knowledge of what
the receiver supports, and quite often the sender cannot even open a
TCP connection to church since there is a spam filter provider in the
way.
BTW, idna does not specify how a-labels work for local parts, and
there are two different implementations around, xn-- and xl--.
Arnt
