milter-regex is a sendmail milter plugin that allows to reject mail
based on regular expressions matching SMTP envelope parameters and
mail headers and body.

In order to build milter-regex, sendmail needs to be compiled with
milter support, installing the libmilter library:

	# cd /usr/src/gnu/usr.sbin/sendmail
	# make clean cleandir
	# [set the environment variable WANT_LIBMILTER to 1]
	# make obj && make && make install