It's already there. Why else do we have the Approved: header?
I know that means a bit of work for the spam cancellers: anything posted
to news.answers should be cancelled if it doesn't have a variant of
'news-answers-request@MIT.EDU' in the approved header; if that does
appear in 'Approved:' in addition to at least one '*.answers' newsgroup,
the message should not be cancelled even if it exceeds some other
limitation.
I think the cancellers and writers of spam cancel software have to take
this into consideration. We use some of our valuable time maintaining
our FAQ documents; it's extremely annoying if the FAQ postings get
cancelled. The FAQ is there for a purpose.
-- Mike Dimmick