Bounce problems and spam filters?

EZMLM fans and experts:

We maintain about 200 mailing lists that are owned by user alias.  We 
have been having troubles where everyone on the list gets bounce warning 
messages.  That shouldn't happen, should it?  When I was doing 
preliminary investigation of this a couple of months ago, Bruce Guenter 
suggested:
> In the "bounce/d" directory of the mailing list itself are copies of the
> bounces to the mailing list.  You can look at these for fuller
> explanations from the receiving or relaying servers why the messages
> bounced.
>   
That was certainly a useful tip because I hadn't been aware of the 
existence and use of the bounce/d directory. With that information, I 
have been able to find and do some cleanup of some of the bad 
subscriptions that are getting bounced ... however, in a number of 
cases, I have gone in after getting one of these bounce warning messages 
and found that there is nothing in the bounce/d directory.

I finally noticed that I have 2 different sets of permissions on these 
directories and suspect that this may be part of the problem.  While I 
didn't knowingly change them, they were clearly changed at some point 
.... and, to make matters worse, they are not the simple rwx permissions 
that I'm familiar with .... they seem to have "S" permissions in the 
group permissions which is one of those things that always has me 
scratching my head.
For example, here are the directory permissions of the mailing lists 
named access and accounting:

drwxr-sr-x  3 alias nofiles 4096 Dec  9 07:49 access/bounce/d