LeeAnne,
We want our old Yahoo files and messages available for anyone to read
but do not want anyone posting there so we close the messages.
However it seems there is some back door that is allowing spammers to
get messages through.
A couple thoughts:
How did you "close" the messages? By changing the "Messages-Who can post" setting in the Access Control page your group's Control Panel? That should be more effective than putting the group on moderation.
One old spammer trick is to set events with reminders in the group's Calendar. Those can continue posting even when the member has been removed or banned. But setting the member's Posting Privilege to the "Override - posts are moderated" setting usually quenches them.
Another trick is to send to the members directly (having collected a list of active members via their postings). If the spam messages do not appear in the group's archive this is what I'd suspect.
Shal
Shal Farley