prevent spammers to use owner list address

hello,
   I have a closed list but somehow the spammers are using the owner of the list address which gets to the list owner. Sample setup of a list.
So in this setup, the spammer insstead of using [email protected]
he's using [email protected]. How can I configure majordomo,
so that he cannot send message to the owner directly.



testonly: "|/usr/local/majordomo/wrapper resend -a /usr/local/mail/lists/testonly.pa
sswd -l testonly -h my.testdomain.com -r testonly -f testonly-owner testonly-outgoing"
owner-testonly: testonly-owner
testonly-request: "|/usr/local/majordomo/wrapper request-answer testonly"
testonly-outgoing: :include:/usr/local/mail/lists/testonly
owner-testonly-request: testonly-owner
testonly-owner: [email protected]
testonly-approval: [email protected]

Thanks.