bug#51733: 27.1; Detect impossible email addresses better

[Lars Ingebrigtsen]

Eli Zaretskii <eliz@gnu.org> writes:

> But From is not the only place where a suspicious address could hide.
> It could also be in the body, or in the quotation parts.  We cannot
> rely on header decoding alone to do this job well.

The scope of the relevant implemented functions are to determine if the
(on-wire) mail headers are suspicious or not, and do so reliably.  We
can add a slew of other functions for other types of DWIM
suspiciousness, of course, but that's outside the remit.

(For instance, if you wish to implement a filter that looks for
suspicious emails, you'd typically find anything that looks like an
email, see whether it can be RFC2047 encoded, encode it, and then call
the -email-suspicious-p function.)

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   bloggy blog: http://lars.ingebrigtsen.no