Note, this method is deprecated, in favor of using spamdyke.
Download qmail-greyd and configure it
# cd /var/qmail/bin
# wget http://thomas.mangin.me.uk/data/source/qmail-greyd
# chmod +x qmail-greyd
# mkdir /var/qmail/grey
# chown vpopmail.vchkpw /var/qmail/grey
Add ,GREY=”" to /etc/tcprules.d/tcp.smtp
# vi /etc/tcprules/tcp.smtp
:allow,BADMIMETYPE="",BADLOADERTYPE="M",CHKUSER_RCPTLIMIT="100",CHKUSER_WRONGRCPTLIMIT="20",QMAILQUEUE="/var/qmail/bin/simscan",NOP0FCHECK="1",GREY=""
Add GREYD paramater to /var/qmail/supervise/smtp/run
vi /var/qmail/supervise/smtp/run
#!/bin/sh
QMAILDUID=`id -u vpopmail`
NOFILESGID=`id -g vpopmail`
MAXSMTPD=`cat /var/qmail/control/concurrencyincoming`
BLACKLIST=`cat /var/qmail/control/blacklists`
SMTPD="/var/qmail/bin/qmail-smtpd"
TCP_CDB="/etc/tcprules.d/tcp.smtp.cdb"
RBLSMTPD="/usr/bin/rblsmtpd"
HOSTNAME=`hostname`
VCHKPW="/home/vpopmail/bin/vchkpw"
REQUIRE_AUTH=0
GREYD="/var/qmail/bin/qmail-greyd"
exec /usr/bin/softlimit -m 27000000 \
/usr/bin/tcpserver -v -R -H -l $HOSTNAME -x $TCP_CDB -c "$MAXSMTPD" \
-u "$QMAILDUID" -g "$NOFILESGID" 0 smtp \
$GREYD $RBLSMTPD $BLACKLIST $SMTPD $VCHKPW /bin/true 2>&1
Rebuild tcprules and restart qmail
qmailctl cdb
qmailctl stop && sleep 2 && qmailctl start