The real problem is that programmers have spent far too much time worrying about efficiency in the wrong places and at the wrong times; premature optimization is the root of all evil (or at least most of it) in programming. (Donald Knuth)
Kerio Mail Server supports looking up in blacklist databases
to identify known spammers. You'll find this under the "Blacklists"
tab at Configuration->Content Filter->Spam Filter. Enabling
the Internet blacklists will cut down on your spam load by a large
However, there are down sides. First, you really need to
be using IMAP or Webmail if you are doing any server side spam
filtering because POP3 doesn't give you access to the default folder
that Kerio moves spam to. You can change that default server side rule
(access your account with Webmail to do so), but that leaves
your Inbox cluttered with **SPAM** messages. You could
then define a default rule in your mail client (Outlook, etc.)
that would squirrel these away somewhere, but why fill up
your hard drive with what is surely almost completely junk?
Note this important point aboout server side rules.
Although you need Webmail to define server side rules, these
rules affect all email as it arives at the users mail box. Rules
defined in Webmail affect mail picked up by POP3 or any other
The reason you need access to the spam is that sometimes
it isn't spam: aggressive spam filters incorrectly identify
mail that you want to see. That's very apt to be true
with blacklists: for example, I use Gmail to send mail, but
Gmail often appears on one or more blacklists. If you
want to be sure to recieve my emails, you have to
whitelist my address when using blacklist lookups.
The default action for blacklisted mail is to block it
entirely. You probably want to change that to instead increase
its Spam score by enough so that it will always be seen as spam.
That setting lets you whitelist by adding custom rules at the first
tab of Configuration->Content Filter->Spam Filter. For
whitelisting a particular sender, you'd add a rule that says
"From" "contains address" "email@example.com" is to be treated as
non-spam. That will allow their mail to get through. Important: if you
have not changed the default "block" for the blacklist
database lookups, the whitelisting will not work!