We recently purchased and implemented the Mail Gateway 5.5 but have only been able to filter spam based on blacklists. Here are the rules I have set in the smtpgw.access section but am looking to find any tips, tricks, or suggestions on what we can do to further block the large amount of spam we still receive.

[smtpgw.access]
RelayRule=allow from any to *@schools.org
ConnectRule=deny from in_dnsbl to *
HeloRule=allow from any to *
MailfromRule=allow from any to *
DNSBlackList=cbl.abuseat.org
DNSBlackList=list.dsbl.org
DNSBlackList=dnsbl.sorbs.net
ConnectRule=allow from any to *
DNSBlackList=dnsbl.njabl.org
DNSBlackList=bl.spamcop.net
RelayRule=deny from any to *

I have tried setting the following connect rule which was filtering a large amount of spam, but due to several misconfigured e-mail clients and/or servers, we were also filtering a large amount of legitimate messages.

ConnectRule=deny from no_name to *

Thanks so much for any help or suggestions you may be able to provide.

Hi there and welcome,

Besides access rules you mentioned (both static and dnsbl) Kaspersky Mail Gateway contains the spam filtering module similar to Kasperky Anti-Spam product, which uses periodically updated spam signature bases, heuristics, recognizes spam in the graphical images, etc.
Perhaps your license simply does not allow you to switch on antispam module - it's not clear from your message why you did not mention antispam engine at all...