Looking into logs i notice a lot of messages like:
16:06:17.180954500 2599 hosts_allow plugin (pre-connection): Too many connections from (local_IP_of_Antispam_Box): 6 > 5Denying connection.
If you look at the code for the host_allow plugin, you'll see some documentation:
...
The B<hosts_allow> module decides before the SMTP-Greeting if a host is
allowed to connect. It checks for too many (running) connections from one
host (see -m/--max-from-ip options in qpsmtpd-forkserver) and the config
file I<hosts_allow>.
The plugin takes no arguments.
...
If you look in /service/qpsmtpd/run you will see:
...
exec /usr/local/bin/softlimit -d ${SOFTLIMIT:-25000000} -s ${SOFTLIMIT:-25000000} -l ${SOFTLIMIT:-25000000} \
/usr/bin/qpsmtpd-forkserver \
-u qpsmtpd \
-l 0.0.0.0 \
-p ${PORT:-25} \
-c ${INSTANCES:-40} \
-m ${INSTANCES_PER_IP:-5}
...
which points you to "INSTANCES_PER_IP". You'll see that is set by template file, from /root/etc/e-smith/templates/var/service/qpsmtpd/runenv/INSTANCES_PER_IP:
{
return "INSTANCES_PER_IP=" . ($smtpd{InstancesPerIP} || "5");
}
So if you do:
config setprop smtpd InstancesPerIP 40
expand-template /var/service/qpsmtpd/runenv
sv t /service/qpsmtpd
you should see a change in your system's behaviour. I suspect you only did the first of those three steps. Changing the properties in the configuration database isn't sufficient - you need to activate the changes by expanding templates and restarting services.