On Sat, 24 Jan 2015, "Jan N. Klug" <jan.n.klug@rub.de> wrote:
> On Sat, Jan 24, 2015 at 04:21:06PM +0100, Stefano Zacchiroli wrote:
>> On Sat, Jan 24, 2015 at 04:59:16PM +0200, Jani Nikula wrote:
>> > On Sat, 24 Jan 2015, Stefano Zacchiroli <zack@upsilon.cc> wrote:
>> > > To do the above, rewrite get_message_id() to scan the current message
>> > > line by line, incrementally computing a SHA1. As a consequence, drop
>> > > the dependency on Mail::Internet.
>> > 
>> > I am not so sure this is a good idea however, see below.
>> [...]
>> But I didn't think of header folding, and you're absolutely correct in
>> saying that might be a problem.
>
> I disagree. I do not think that header folding is a problem here. RFC
> 5322 and RFC 2822 state that FWS in the message-id are not allowed (as
> opposed to In-Reply: and other headers, where FWS may occur between, but
> not inside message-ids).

Not *inside* message-ids, but as a data point, 0.05% of my email have
FWS *before* the message-id. That's more than the amount of messages
I have without a message-id.

BR,
Jani.