To configure MIMEDefang, you have to edit the file /etc/mail/mimedefang-filter.
This is a Perl source file, so you have to know Perl. Go ahead and read the man
pages mimedefang(8), mimedefang.pl(8) and mimedefang-filter(5). There are some
sample filters in the /usr/share/doc/mimedefang-* directory.

In order to complete the installation of MIMEDefang, you will need to add for
example the following lines to your /etc/mail/sendmail.mc file:

  define(`MILTER', `1')dnl
  define(`confMILTER_LOG_LEVEL', `6')dnl
  INPUT_MAIL_FILTER(`mimedefang', `S=unix:/var/spool/MIMEDefang/mimedefang.sock, F=T, T=S:1m;R:1m;E:5m')dnl

Use "service sendmail restart" to rebuild your /etc/mail/sendmail.cf file, run
"chkconfig --level 2345 on" to start MIMEDefang during booting time per default
and execute "service mimedefang start" to start the service. When everything
was correct, MIMEDefang should now do its job...