[Mimedefang] Need help understand whitelisting (whitelist_from_rcvd)

[Steve Pfister]

I'm trying to add whitelist_from_rcvd to our setup (mimedefang 2.41 +
spamassassin 2.63), mainly because of problems with internal users sending
to other internal users.

We have spamassassin adding a header 'X-Spam-Status: YES' if the message
exceeds the threshold, then procmail filters the mssage to a file in the
user's home directory if the header is present.

I've tried whitelist_from_rcvd in:

/etc/mail/spamassassin/local.cf
/etc/mail/spamassassin/sa-mimedefang.cf
/home/mimedefang/.spamassassin/user_prefs

(...and have stopped/started sendmail and mimedefang each time...)

but nothing seems to be happening. I can't tell if the whitelisting isn't
working, or it is working and procmail is filtering it anyway.

What exactly does whitelisting do to the message? Can I tell if the given
message was whitelisted? Can I maybe add a header that procmail can check
for?

--Steve