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