Any list that is SEND= PUBLIC, is subject to the random act of spam. Any
list that is SEND= PRIVATE but SUBSCRIPTION= OPEN, is subject to a
spoofing spammer.
The lists that I operate tend to have:
* Subscription= OPEN,CONFIRM
* Send= PRIVATE or sometimes EDITOR, where EDITOR= me,(listname)
On one list with higher anti-spam requirements, we also have
* DEFAULT-OPTIONS= REVIEW
with my issuing
QUIET SET listname NOREVIEW FOR new_subscriber
as required.
Your Mileage May Vary.
Many other techiques are discussed on the anti-SPAM list SPAM-L.
Archives and FAQ available.
Sub Instruct.: http://oasis.ot.com/~dmuth/spam-l/#spam-l-subscribe
/Pete