Sendmail help needed... How to reject domains that contain "opt-in" or "offers"..

[Apolinaras Sinkevicius <apsinkus yahoo com>]

I have followed the "spam flow" to my mail server and
found that if I could reject senders whos domain
contains "optin", "offer" and etc. I would cut 75% of
spam. Is there any way to write that rule?

Thanks

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