I think it would be useful to appoint a few folks to 'manager' status.
I am prepared to take on some admin responsibilities and ensure that
the site is being used appropriately. Who currently has 'owner' status
for the group?
A search about managing spam in Google Groups led to this useful post
thread. I have reproduced the relevant section below.
http://groups.google.com/group/Google-Groups-Basics/browse_thread/thread/7bb85f4df3825a93/7f3eb6beccdf1ebd
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Seemingly spammers are becoming able to bypass group safety settings
when the groups are on Anyone can join, or Anyone can post, and/or All
messages are held for moderation.
Till now, these settings seem safe:
* Under "Who can join?" select "People can request an invitation to
join"
* Under "Who can post messages?" select "Members only"
* Under "Message moderation" select "Messages from new members are
moderated"
If you don't like these settings, and you're spammed, an alternative
could be to quickly add and ban the spammer. At least, he will be
blocked as possible sender, hopefully forever.