bug#51733: 27.1; Detect impossible email addresses better

[Lars Ingebrigtsen]

積丹尼 Dan Jacobson <jidanni@jidanni.org> writes:

> Upon sending,
> To: Bob_Norbolwits@GCSsafetyACE.com​
> should trigger a warning:
> "You won't get far trying to send mail with ZERO WIDTH SPACE in an address,"
> instead of blundering along and sending to "gcssafetyace.xn--com-7m0a"!!

I guess Emacs should run all email addresses through a check for
Unicode confusability and direction markers and all that stuff, too.
(Which got a lot of work lately in a display context.)

Do we have a predicate somewhere that says whether a string is suspicious
based on confusables and r2l markers and stuff?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no