[Mimedefang] configuring mimedefang-filter to reject during smtp

[Tony]

I've installed mimedefang 2.67 on a raq550 running strongbolt2 (Centos
4.8) and I need to configure it so it rejects spam during the smtp
process. I've installed spamassassin and that seems to be working fine
and I've got the INPUT_MAIL_FILTER entry in sendmail, I understand that
mimedefang-filter is the place to do the configuring but it looks
complicated and as a newbie I'm worried about making a mess of it.
Can anyone provide a mimedefang-filter example that shows the correct
syntax to reject during smtp? I did a search on google before posting
this but couldn't find an example that fitted the syntax in the
mimedefang-filter file I have. In the mimedefang-filter file I see
entries to change the header and do this and that but all I'm intetested
in is rejecting during smtp. Thanks for any advice.