[exim] How to drop emails from phantom user

Hi,

I receive a lot of mails from several spammers that hides the real sender, for example, the from field, may be:

From: "SomeText In the from field" <someuser@???>

I want to drop all emails received that have "SomeText" or "sometext" or any combination of cases.

Can anyone help me and say me what and where I must to put in configure exim file?

And, If I want to apply the same restriction but only to one account under my virtualhost?

Thanks in advance.

Jorge Colaccini