Ronald F. Guilmette wrote:
These days, whenever one builds any kind of tool that does
anything with e-mail, it is necessary to think about this
new-fangled phenomenon of Internationalized Domain Names,
so...
In what (if any) mail headers generated by Postfix might one
reasonably expect to find either (a) "punycoded" domain names
or else (b) Unicode characters.
I don't think that currently Postfix does any conversions
between ASCII-compatible encoding (ACE) and UTF-8 forms
of a domain name, so both forms could be seen in a mail
header with SMTPUTF8 enabled, and ACE forms would be seen in a
traditional setup (but possibly also UTF-8 forms and arbitrary
non-ASCII junk, despite not being legitimate).
Docs says (SMTPUTF8_README):
The initial Postfix SMTPUTF8 implementation performs no automatic
conversions on UTF8 strings beyond what is needed to perform DNS
lookups.
Header fields carrying a domain name (that come to mind) are:
Return-Path, Received, (Resent-)Sender, (Resent-)From, (Resent-)To,
(Resent-)Cc, Reply-To, (Resent-)Message-ID, In-Reply-To, References,
DKIM-Signature, DomainKey-Signature, List-*, potentially any X-*,
and I'm sure there are others (Content-Location ?, ...).
And of course, I have the same two questions with respect to
the requests that are sent from Postfix to any installed and
activated policy server. Within that stuff, where might one
expect to see either (a) punycode or else (b) Unicode?
Any of these, which can appear in a mail message.
No conversions by MTA for the time being.
Btw, amavisd since 2.10.0 converts ACE domain names to UTF-8
for presentation purposes (logging, JSON structured report,
DNS and admin notfications), and encodes non-ASCII UTF-8 domains
in sender and recipient addresses into ACE if the next hop MTA
(e.g. back-end postfix) does *not* announce support for SMTPUTF8.
P.S. Now that I have skimmed, briefly, the RFCs relating to this
new SMTPUTF8 extension, I do have a question about that. But it
seems like it would be inappropriate and off-topic for me to post
that here, since it is not in any way Postfix-specific. Where are
RFCs (such as RFC 6531) normally discussed?
Try these:
ietf-smtp -- Discussion of issues related
to Simple Mail Transfer Protocol (SMTP)
https://www.ietf.org/mailman/listinfo/ietf-smtp
IMA -- EAI (Email Address Internationalization)
https://www.ietf.org/mailman/listinfo/ima
Mark
