>>I don't think that will help with the spam messages.  They won't appear
>>while the list is being held, but as soon as you free the list, all
>>the held messages will be processed.

That is correct (but see below).

Perhaps the best way might be to set the list to "Send= Owner,Confirm",
which will reject postings from anyone but the list owner.  Unfortunately
you can't modify the response from LISTSERV but if you warn your legitimate
subscribers first, there shouldn't be any problem.

You could also simply set the list up for moderation and reject anything
that looks like a spam.  Note that if you want to shut down the list for
a while (e.g., you're going on holiday), you might want to set the list up
to be moderated and then HOLD it. When you get back and send the FREE command,
all of the held messages will still be there but will all have to be
approved before they can be distributed.  This might mean a lot of work
when you get back but at least you can keep the obvious spam from going
through.  You can also use this trick if a flame war starts on your list
and you want to institute a "cooling down" period before you allow postings
to go through again.

>I believe that if you just LOCK the list, it will reject all messages
>that anyone attempts to post to it.

No.  Locking the list (by doing a GET without (NOLOCK ) only locks the
header and the subscriber list.  It does not stop people from posting
to the list.

Nathan