I know these are a bit late, but:
1. RFC-822 specifically says that cntl-H should be used to give overstrike
semantics. In fact I don't know of any mail readers which obey this aspect
of rfc-822 except perhaps when used on an LA34. So I think in the section
which discusses the meaning and non-meaning of control characters it should
explicitly cancel this aspect of rfc-822 which is in abeyance, particularly
as rfc-xxxx provides much better mechanisms for representing things like an
O with a / through it.
2. RFC-821 describes a mechanism for transporting a message with a line with
a single "." in it. Putting that in rfc-821 now looks wrong. The correct
approach is for rfc-821 to say "this mechanism can only be used to transport
messages in which a single period on a line by itself is encoded away or
is not allowed." The act of dot-doubling to comply with this is an
encoding rule in the 7bit Content-TransportEncoding of rfc-xxxx (and of
the 8bit encoding). This encoding rule is not needed in base64 or
quoted-printable encodings.
It is pretty important that we distinguish carefully between the encoded
and unencoded messages if things like John Klensin's SIZE command are
to be introduced into SMTP. However you don't have to support the SIZE
command to support the idea of making this distinction in this way.
Bob Smart