Block spam message without sender address

[keith]

Dear All,
My client was tell to me , they always receive a large volume of spam message
is no sender address, how I can block this type of message in MS, I checked
the filename rules and the mailing archive said is related the Watermark
feature, but still no idea, who can tell me how to do this.

My MS is version 4.63 with spamassassin + DCC + pyzor + razor + Clamav +
Kaspersky

Thanks
Keith 

--