[exim] Discard mails via exim filter

Hi,

Is there any way I can discard mails via exim filter?

Context: I am trying to discard mails on the basis of spam keywords.
Something like as shown below:

-------------------
if $header_subject: contains "Viagra"
then
<discard mail with message Mail rejected due to spam keywords>
fi
---------------------

I tried with 'fail text' and 'logwrite'.

* With fail text: a bounce back mail is as well sent, which is not required
in my setup
* With 'logwrite' : The permission of exim mainlog file is to be changed
[/var/log/exim_mainlog] to 0644 [now its 0640].

Please let me know how I can discard the message [with just a message be
written to log and no bounce back].

In exim configuration we can use " discard message = xyz ". Is there any
similar way which we can use in exim filter file as well.


--
Regards,
Soumya