I installed mailman with htdig with:
	cd /usr/ports/mail/malman
	make config
		- add HTDIG
	make install

I set things up and ran ~mailman/cron/nightly_htdig.  It failed
when running ~mailman/cron/rundig because the paths in ~mailman/cron/rundig
were not updated.

I fixed the paths in ~mailman/cron/rundig to match the paths in
/usr/local/bin/rundig and then things worked.

% cd ~mailman
% diff -u cron/rundig.orig cron/rundig
--- cron/rundig.orig	2019-06-08 18:53:23.120474000 -0400
+++ cron/rundig	2019-06-08 22:15:45.675837000 -0400
@@ -7,10 +7,10 @@
 #
 # This is a sample script to create a search database for ht://Dig.
 #
-DBDIR=/opt/www/var/htdig
-COMMONDIR=/opt/www/share/htdig
-BINDIR=/opt/www/bin
-conffile=/opt/www/conf/htdig.conf
+DBDIR=/usr/local/share/htdig/database
+COMMONDIR=/usr/local/share/htdig/common
+BINDIR=/usr/local/bin
+conffile=/usr/local/etc/htdig/htdig.conf
 
 # To help debug problems, try running rundig -vvv
 # This will add lots of debugging output to all of the programs



% pkg which ~mailman/cron/rundig
/usr/local/mailman/cron/rundig was installed by package mailman-with-htdig-2.1.29_5
% pkg which /usr/local/bin/rundig 
/usr/local/bin/rundig was installed by package htdig-3.2.0.b6_6
% uname -a
FreeBSD mail 11.2-RELEASE-p10 FreeBSD 11.2-RELEASE-p10 #0: Mon May 13 21:20:50 UTC 2019 root@amd64-builder.daemonology.net:/usr/obj/usr/src/sys/GENERIC  amd64