bug#51733: 27.1; Detect impossible email addresses better

[Eli Zaretskii]

> From: Michael Albinus <michael.albinus@gmx.de>
> Cc: Lars Ingebrigtsen <larsi@gnus.org>,  51733@debbugs.gnu.org
> Date: Wed, 19 Jan 2022 13:49:56 +0100
> 
> > Perhaps also Tramp (host names)?
> 
> --8<---------------cut here---------------start------------->8---
> (defconst tramp-host-regexp "[[:alnum:]_.%-]+"
>   "Regexp matching host names.")
> 
> ;; The following regexp is a bit sloppy.  But it shall serve our
> ;; purposes.  It covers also IPv4 mapped IPv6 addresses, like in
> ;; "::ffff:192.168.0.1".
> (defconst tramp-ipv6-regexp "\\(?:[[:alnum:]]*:\\)+[[:alnum:].]+"
>   "Regexp matching IPv6 addresses.")
> --8<---------------cut here---------------end--------------->8---
> 
> This should be sufficient, shouldn't it?

If this isn't too restrictive, sure.