Re: [art] Question on RFC 8823

[Alexey Melnikov <[e-mail]>]

Hi Ned,

On 06/05/2021 20:49, Ned Freed wrote:

>> Hi Steffen,
>
>> Thank you for your comments on RFC 8823. My replies below.
>
>> ...
>
>> > While reading it i was astonished to see RFC 2231 not RFC 2047
>> > mentioned for header field content (as opposed to field parameter
>> > value content that does not occur here since all the value is
>> > a base64url encoded string, see for example 3.1.1 -- i mean, yes!,
>> > RFC 2231 is a straight good one compared to the older RFC 2047,
>> > but it does not replace it), and the use of MIME in general even
>> > for plain US-ASCII mails (without overlong lines and any other
>> > such pitfalls which would qualify for using MIME in an RFC 5322
>> > internet message).
>
>> If you are talking about encoded word construct used in Subject header
>> field, then RFC 2231 is backward compatible with RFC 2047 encoding, so
>> any RFC 2047 encoded words are also valid RFC 2231 encoded words.
>
> But not vice versa, which is why, in the unlikely event someone 
> actually uses
> the RFC 2231 extension, it will work.
>
> Specifically, RFC 2231 adds an optional language tag to the charset
> part of an encoded word. If that feature is used and only RFC 2047
> forms are supported the charset field isn't going to match.
Actually, I suspect there is more than one parser that is able to parse 
RFC 2231 syntax, but ignores the language tag.
> That said, if RFC 8823 is ever updated, it might be a good idea to say 
> what to
> do with the language tag: Don't generate it and if you find one, 
> ignore it.
Agreed.
>> The document requires support for RFC 2231 in order to have 
>> compatibility
>> with most existing email clients.
>
> There's a client that actually generates a language tag in an encoded 
> word?
> Wow. I don't think I've ever seen one in the wild.

I thought I've seen some, but a quick check of my INBOX archive for the 
last 3 years doesn't have any examples.

Best Regards,

Alexey