Specifically, all mail sent to namedroppers is:
1) first run through spamassassin. Mail that is rejected here is not
archived, as the number of such messages is large. All mail sent to
mailing lists on the server hosting namedroppers is run though
spamassassin, so this is not a namedroppers-specific procedure.
SpamAssissin needs to be shot. Most of its criteria are really poorly chosen.
Even if its criteria are good at identifying spam on a large scale (with few
false positives) that doesn't mean they will work well for a narrowly-focused
discussion. In my experience SpamAssassin has too high a false positive rate
to be trusted without human review as a backup.
p.s. regarding messages that did not make it to the namedroppers archive -
are the IETF archives still using to/cc message headers to decide which
archive a message should be stored in? if so, is it possible that a message
which was sent to multiple lists might be archived in only one of those lists?