SpamAssassin

First links to documentation:

Install SpamAssassin

Dependencies:

yum -y install perl-ExtUtils-MakeMaker perl-Digest-SHA perl-Net-DNS perl-NetAddr-IP perl-Archive-Tar perl-IO-Zlib perl-Digest-SHA perl-Mail-SPF \
perl-IP-Country perl-Razor2 perl-Net-Ident perl-IO-Socket-INET6 perl-IO-Socket-SSL perl-Mail-DKIM perl-DBI perl-Encode-Detect perl-HTML-Parser \
perl-HTML-Tagset perl-Time-HiRes perl-libwww-perl perl-Sys-Syslog perl-DB_File perl-Razor-Agent pyzor

Additional CentOS7 packages:

yum install perl-Net-CIDR* perl-Net-DNS-Nameserver perl-Net-Patricia perl-Geo-IP perl-Digest-Sha1

CustomBuild:

cd /usr/local/directadmin/custombuild
./build set spamd spamassassin
./build spamassassin

Enable by default: Create/Edit /usr/local/directadmin/scripts/custom/user_create_post.sh

#!/bin/sh
if [ "$spam" = "ON" ]; then
   DIR=/home/$username/.spamassassin
   mkdir  $DIR
   touch $DIR/user_prefs             #or this is where you'd copy  the default user_prefs you want them to have, instead of "touch".
   chown  ${username}:mail $DIR
   chmod 771 $DIR
   chown $username:$username  $DIR/user_prefs
   chmod 755 $DIR/user_prefs
   touch $DIR/spam
   chown  mail:$username $DIR/spam
   chmod 660 $DIR/spam
fi
exit 0;

Set default action: Create/Edit /usr/local/directadmin/scripts/custom/domain_create_post.sh

#!/bin/sh
F=/etc/virtual/$domain/filter.conf
if [ -e $F ]; then
   echo "where=userspamfolder" >> $F
   echo "action=rewrite&value=filter&user=$username" >> /usr/local/directadmin/data/task.queue
fi