Please note, that the mailshield only scans "new" emails i.e. mails that are coming through the network to your mail client. Thus only mails that were received after you turned SSL off in your mail client can show up in the statistic.
If you still see a value of 0 even when new mails have arrived, please post here (or send to my email) the output of the following command written to the console (terminal application):
cat /var/log/system.log | grep 'proxy\[[0-9]*\]'