We must get the perl libraries from CPAN/ports, to make things easier this should be as simple as copy/paste, if only. The shell you are using may not be able to handle a whole lot in one go, so you could make a short script to run it all.

pkg_add ftp://ftp.openbsd.org/pub/OpenBSD/3.7/packages/i386/p5-Digest-SHA1-2.10.tgz
pkg_add ftp://ftp.openbsd.org/pub/OpenBSD/3.7/packages/i386/p5-Digest-HMAC-1.01.tgz
pkg_add ftp://ftp.openbsd.org/pub/OpenBSD/3.7/packages/i386/p5-Net-DNS-0.47.tgz
pkg_add ftp://ftp.openbsd.org/pub/OpenBSD/3.7/packages/i386/p5-HTML-Tagset-3.04.tgz
pkg_add ftp://ftp.openbsd.org/pub/OpenBSD/3.7/packages/i386/p5-HTML-Parser-3.45.tgz
pkg_add ftp://ftp.openbsd.org/pub/OpenBSD/3.7/packages/i386/p5-Mail-SpamAssassin-3.0.2.tgz


cd /downloads
wget http://search.cpan.org/CPAN/authors/id/D/DS/DSCHWEI/Parse-Syslog-1.03.tar.gz
tar zxvf Parse-Syslog-1.03.tar.gz
cd Parse-Syslog-1.03
perl Makefile.PL ; make test install

cd /downloads
wget http://search.cpan.org/CPAN/authors/id/M/MI/MIKEK/Statistics-Distributions-1.02.tar.gz
tar zxvf Statistics-Distributions-1.02.tar.gz
cd Statistics-Distributions-1.02
perl Makefile.PL
make test install

Now we can make clam

But first create users that we require.

groupadd clamav
groupadd qscand
mkdir /var/spool/qmailscan
useradd -c "Qmail-Scanner Account" -g qscand -d /var/spool/qmailscan -s /bin/false qscand
useradd -d /var/empty -s /sbin/nologin spamc
useradd -d /tmp -s /sbin/nologin clamav
groupadd vchkpw

cd /downloads/qmailrocks
tar zxvf clamav-0.80.tar.gz
cd clamav-0.80

These variables need to be exported so that configure knows how to build the makefile

export LDFLAGS="-L/usr/local/lib -lpthread"
export CFLAGS="-I/usr/local/include"

./configure --disable-clamav \
--enable-dependency-tracking \
--disable-clamuko \
--enable-bigstack \
--sysconfdir=/etc \
--with-user=clamav \
--with-group=clamav \
--disable-cr 

make
make check
make install
make clean

Now that is all done we must change the config,

vi /etc/clamd.conf

Change

Example

to 

#Example

Make sure LogFile is

LogFile /var/log/clamav/clamd.log

And that LogSyslog is not commented

Also make sure User is <b>qscand</b>

DatabaseDirectory should be 

DatabaseDirectory /usr/local/lib/clamav

And finally ScanMail should not be commented, now save and exit vi.

We need an rc control file for clam, if you copy and paste this:

OUTP="#!/bin/sh\n"
OUTP=$OUTP"FOO_BIN=/usr/local/sbin/clamd\n"

OUTP=$OUTP"test -x \$FOO_BIN || exit 5\n"

OUTP=$OUTP"case \"\$1\" in\n"
OUTP=$OUTP"start)\n"
OUTP=$OUTP"echo \"Starting \`\$FOO_BIN -V\`\"\n"
OUTP=$OUTP"\$FOO_BIN\n"

OUTP=$OUTP";;\n"
OUTP=$OUTP"stop)\n"
OUTP=$OUTP"echo \"Shutting down \`\$FOO_BIN -V\`\"\n"
OUTP=$OUTP"killall \$FOO_BIN\n"

OUTP=$OUTP";;\n"
OUTP=$OUTP"restart)\n"
OUTP=$OUTP"\$0 stop\n"
OUTP=$OUTP"\$0 start\n"

OUTP=$OUTP";;\n"
OUTP=$OUTP"*)\n"
OUTP=$OUTP"echo \"Usage: \$0 {start|stop|restart}\"\n"
OUTP=$OUTP"exit 1\n"
OUTP=$OUTP";;\n"
OUTP=$OUTP"esac\n"
echo $OUTP > /usr/local/etc/rc.d/clamd.sh

We need to make some changes to the freshclam conf file, so

vi /etc/freshclam.conf

Make sure Example is commented,

LogSyslog should also be uncommented 

DatabaseDirectory should be DatabaseDirectory /usr/local/lib/clamav

We must make a couple of directories for clamav

mkdir -p /var/log/clamav
mkdir -p /usr/local/lib/clamav

Give ownership to clamav

chown -R clamav.clamav /var/log/clamav /usr/local/lib/clamav

Now update the definitions:

/usr/local/bin/freshclam

Lets put a couple of values in /etc/mail/spamassassin/local.cf

echo "rewrite_subject 1"  >> /etc/mail/spamassassin/local.cf
echo "required_hits 5"  >> /etc/mail/spamassassin/local.cf

Now lets get spamd and greylisting enabled in /etc/rc.conf, change

spamd_flags=NO and spamd_grey=NO

to

spamd_flags=YES and spamd_grey=YES

Make sure that spamd/clamd start at system boot by adding the following lines to /etc/rc.local:

csh -cf '/usr/local/bin/spamd -L -x -u spamc &'
csh -cf '/usr/local/sbin/clamd &'