[idn] IDNs and email

[Andrew Draper <ADRAPER@altera.com>]

Looking at the charter I can't see any reason why an IDN protocol candidate
shouldn't be allowed to suggest changes to SMTP (or other protocols) as well
as to the DNS protocol.  Of course those changes should be as minimal as
possible.

Some of the IDN candidates (UTF-5 and CIDNUC) allow international characters
to the right of the @ sign while keeping the email infrastructure working.
I suspect, however, that users would want to be allowed to use international
characters anywhere in an email address, not just to the right of the @
sign.

For the UTF-8 proposal, or for fully internationalised email addresses with
the other proposals the email system will need to be modified.  To avoid a
flag day there are two requirements on the SNMP modifications:

1) There should be an ASCII-only equivalent email address for each
internationalised email address.  There must be a way for a program to
transform the internationalised address into the ASCII-only form (eg
algorithmically or by doing a lookup somewhere).

Doing the transform algorithmically would be easier, but might not be quite
so good for the user.  Doing it with a lookup (eg for a new type of DNS
record) would be more complicated and generate fractionally more traffic
(compared with the amount needed to send email anyway) but would probably be
more user-friendly.

2) There must be an ESMTP option which indicates that a server supports
internationalised email addresses.  If an internationalised ESMTP client has
an internationalised email, but the server doesn't indicate support then the
client must transform all addresses (in the envelope and in the message
headers) into their ASCII-only equivalent.

In addition it would be nice if an internationalised recipient could
transform the ASCII-only form back into the internationalised form (for
example if the email has been through an ASCII-only relay).

I think this suggests a further requirement for IDN (based on 1 above):

| If an encoding is used which is not mapped into ASCII then there SHOULD
| be an ASCII-only representation of each IDN, and there MUST be a way for
| a program to find the ASCII-only representation (or lack of it) for an
| IDN.

I say SHOULD and not must since if a lookup service is used then an
administrator
might choose not to configure an ASCII-only equivalent for a particular
name.

Regards,

    Andy