Anti Spamming

[FONR]

Hi
Can any one tell me a solution for blocking mails on subject.
I have a customer who gets wierd mails form different sites , the mails
originate from different site everytime , thus i am not able to use the
badmail from feature as it is not a fixed site.
Any clue or help would be highly appreciated.
Thanks in advance
FONR
mailto:[EMAIL PROTECTED]