bug#51733: 27.1; Detect impossible email addresses better

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: 51733@debbugs.gnu.org,  jidanni@jidanni.org
> Date: Mon, 17 Jan 2022 15:54:58 +0100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Yes, I understand the general concern, but I'm asking how serious is
> > this in practice.  Can you tell?
> 
> I don't know how to quantity that.  We're talking about security
> mechanisms, and they should be reliable.

Well, now that I know the answer, I don't think it's hard to quantify.
But maybe I'm missing something.

> (But, yes, the differences are massive, especially in the Asian parts of
> the data.)

I don't think I understand what you mean by "the Asian parts".  Do you
mean the CJK parts where we lump several scripts together into 'han'
and 'kana'?

> It's impossible to implement the Unicode security recommendations based
> on the Blocks.txt data -- it's that simple.

Can you tell more about why it is impossible?  If it's a relatively
simple issue of "translating" the Unicode script names into ours, then
it should be quite simple.  Since you say it's impossible, I guess
there's some factor(s) here that I miss?