Source: http://forum.swsoft.com/printthread.php?threadid=40173

If qmail-smtpd is spawning many processes and comsumming all processing capacity on a server check the name of the *.pem files in /var/qmail/control. If the files are not:

 dh512.pem
 dh1024.pem

Rename them (usually I've seen dhparam512.pem and dhparam1024.pem) accordingly, or, symlink them:

Update PHP to version PHP 5.2.5 while running Plesk? Horde WebMail broken? Log in and become the root system user and run this one-liner, then restart Apache:

# cat > /etc/httpd/conf.d/zz050a_horde_php_patch.conf <<EOF 
<DirectoryMatch /usr/share/psa-horde>
    php_admin_value include_path "/usr/share/psa-horde/lib:/usr/share/psa-horde:/usr/share/psa-horde/pear:."
</DirectoryMatch>
EOF
# service httpd configtest && service httpd graceful

Some discussion:

PHP 5.2.5 introduced a security fix to not allow scripts to override

So you're using the Adding Greylisting support to qmail on Plesk 8|Greylisting support I linked to but you upgraded Plesk and BOOM Greylisting is gone and spam is back, eh? Not to fear! You did leave the source in place, right? If so, just run this script:

<pre> #!/bin/sh cd /root/qmail-1.03 make clean make /etc/rc.d/init.d/qmail stop

cp -f qmail-envelope-scanner /var/qmail/bin/. cp -f qmail-smtpd /var/qmail/bin/. chown root.qmail /var/qmail/bin/qmail-envelope-scanner