On RH9, the $MAIL environment variable could be set in either
/etc/libuser.conf (mailspooldir), /etc/login.defs (MAIL_DIR), or /etc/profile
(MAIL). $MAIL *could* also be set elsewhere, but you can start there for
clues. Irregardless, setting up a recipe to deliver directly to your desired
mail spool should work.
On RH9, the $MAIL environment
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May