On 22/04/15 22:38, Viktor Dukhovni wrote:
> On Wed, Apr 22, 2015 at 09:52:44PM +0100, Jeremy Harris wrote:
>
>>> Question for the Exim team. It seems you have code for converting
>>> UTF-8 localparts to ASCII. What encoding do you use for that?
>>
>> "xn--" <punycode>
>>
>> (i.e. like a domain element)
>
> That's rather unwise IMHO. The "xn--" prefix is only applicable
> to domain names (IDNA), and should not be used to encode localparts.
Not proven.
> If you're going to encode, at least use "xl--", which is already
> in use another MTA.
Why?
You appear to be saying "do it purely because that other MTA
does it".
> In domains, the Punicode encoding is applied one label at a time.
Irrelevant; this is not a domain and it is always known to
not be a domain.
> As you can see there's a bit more to it, because the encoding is:
>
> xl--<PunyCode>
>
> not
>
> xn--<Punycode>.xn--<MorePunycode>...
>
> for each "label" in the localpart (which is not a DNS name).
... and Exim's current coding does, for a localpart,
xn--<punycode>
not xn--<punycode>.xn--<morepunycode>
