[Mailman-Users] Umbrella List Spam Protection

[Links at Momsview]

I currently have a VERY large ( >100k)  announce only list (always
moderated) running mailman  2.1 under Postfix.

For performance reasons I'm considering splitting this list into 26 sublists
based on the first letter of each subscriber email.
I would then use an umbrella list to send to all of the sublists at once.

As I understand it, unless I want to separately approve the message for the
26 sublists I need to allow at least one email address to post unmoderated
on ALL of the sublists.  This is very scary since spammers currently try to
post on my current large list almost daily.



(1) How do I protect the sublists from spammers who spoof the "from" address
in their emails?

(2) Can I protect these sublists from ALL emails other than those from
localhost and my umbrella list?

(3) Are there any other methods that people use for Umbrella announce only
lists?


One other method I've been thinking about is using a grep expression to
define a sender address that is only valid for one day each month.
Any idea how I could do this?