How to deal with mailing list hit by spammers

[Gerardo Ballabio]

Hello,
I'm the administrator of a project hosted on Savannah (galois). As
such I'm also administrator of its mailing list (galois-list).
Recently the list seems to have become a target for spammers.

Posting by non-members is moderated and the moderators are doing an
excellent job (whenever I've logged in to deal with a message,
somebody else had already processed it!).

However, being a list administrator, for every single spam message
posted to the list, I receive a notification message like this on my
personal email address:

-----------
From: galois-list-owner(at)nongnu.org
Subject: Galois-list post from ... requires approval

As list administrator, your authorization is requested for the
following mailing list posting:
[snip]
-----------

I'm getting several dozens of those messages per day.
Is there a way to stop that "indirect spam"? Perhaps a mailman
configuration to turn notifications off?

Thank you
Gerardo