remove from

Hi, I want to avoid people that send e-mails to my
server (Unix server)  with the to:

undisclosed-recipients:;

Any body who can help me ?

I use freebsd
I go to        /etc/mail  (sendmail)
vi access             to avoid certain domains or e-mail addresses

I go to /etc/poisoned  (In procmail)
to avoid certain files : *.exe, *.vbs..... etc..
how to avoid (undisclosed-recipients )

Thanks a lot