I just come from configuring SpamPal on my local Windows machine. The amount of unsolicited mails is tremendous on my main address these days. My hosting service reported me of something like a thousand mails in ten hours. To rise the filter level once more would not make sense, they said and proposed to install SpamPal [1] which taggs spam and makes filtering more easy.
On the other hand you could change your mail policy and make use of a tool like Active Spam Killer [2]. ASK sends a confirmation message back to the unknown sender and keeps the mail pending until the (human) sender confirms the request. ASK is an Open Source solution. A similar service is available through Mailblocks [3].
[1] http://www.spampal.org/usermanual/clients/outlook2000/outlook2000.html
[2] http://www.paganini.net/ask/
[3] http://www.mailblocks.com
