Re: First strawman for UTF-8 headers proposal

Paul Hoffman / IMC <[email protected]> writes:

> All comments welcome!

This proposal appeals to me.  Some comments:

> - The dual motivations are to allow UTF-8 everywhere in the headers and
> to not bounce any messages just because they originated with UTF-8
> headers.
...
> - If a receiving SMTP server does not support UTF-8-HEADERS, the sending
> SMTP client downgrades all headers and continues to send the message.

Following the example of 8BITMIME, I believe implementations should be
allowed to bounce messages if they do not implement the fall back
mechanism.  Otherwise in 20 years, all systems would still be forced
to implement a downgrade mechanism that nobody use or test.  Users
will require that implementors support downgrading today, but
eventually they won't have to bother about it.

> - Free text fields are downgraded using quoted-printable encoding;
> SHOULD be into UTF-8 charset. Downgrading MUST only be done if
> necessary.

Does this intentionally forbid non-QP RFC 2047 encodings?  E.g.,
strings like =?ISO-8859-2?B?dSB1bmRlcnN0YW5kIHRoZSBleGFtcGxlLg==?=.

> - The Address-map: header is downgraded using Base64 for mailbox
> names, IDNA for domain names.
>
> - Example:
>    Address-map: José@example.com,[email protected];
>        törbjørn@fältström.se,tb@fältström.se
> If passed to a non-UTF-8-HEADERS system, this header gets downgraded
> to:
>    Address-map: [email protected],[email protected];
>        [email protected],[email protected]

It might be nice to use the RFC 2047 encoding instead, so that the
header is rendered properly in MIME aware clients.  It would make
cut'n'paste of non-ASCII email addresses possible, even from MUAs that
doesn't support this new standard.  Qualify it to MUST use UTF-8
charset and the "B" encoding if you wish.  A possible disadvantage
would be if gateways converts RFC 2047 data from one charset to
another, although I think the advantages are larger.

> - Other headers that include mailbox names and domain names will need
> further definition for downgrading.

Here there may be dragons.  There are many headers, standard and
non-standard ones, that contain mailboxes, although without using the
RFC 2822 BNF 'mailbox'.  References: is one.  Various List-* headers
are others.

In general, I think the Address-map idea need some further pondering,
especially with regard to modifying in transit and populating them
from address book caches, but also the encoding.

Thanks,
Simon