The mailboxes getting swamped by junk messages these days is not an uncommon scene. We put our email addresses while registering or filling up the Contact Forms of so many websites. Spammers use more sophisticated email harvesting tools that catch these addresses, catalog them into database, perhaps regionwise, Countrywise etc and sell them on CDs too. Perhaps sometimes junk mails keep coming like 'Get CD of 1 Million Addresses'.
The email clients nowadays also come with MessageRules that aide us in filtering out unwanted mails. However, the amount of filtering capability is restricted to the Internet Headers and a limited set of previously stored details regarding the particular sender in question. Fortunately, we have a few Internet Spam Prevention softwares too. The unfortunate thing is that not all are free and some are bulky and some are too tedious to configure.
Of late, I came across a free software called SpamPal, a free Spam Detection software from http://www.spampal.org.uk/ Once the software is installed, you need to configure your mailclient to connect to your mailserver through SpamPal. SpamPal acts similar to a POP-Proxy. As the message downloads, SpamPal activates its plugins one-by-one, making them to act on the mail, its internet headers and the body.
The address and its parent domain, routing IP addresses that the message was relayed through are all checked and verified against standard DNSBL servers. To protect against network getting clogged from multiple and redundant DNSBL queries, the DNSBL queries are remembered for a specified time, that is configurable from the SpamPal Control Panel Applet.
If a message is certified as Spam, the subject of the message is branded as **SPAM** along with an Internet Message Header. Now a message rule in the mail client can be set to delete messages from server without downloading if the subject or Internet Message Header was classifed as **SPAM** as above.
Note: I am just a normal user of SpamPal. I found SpamPal is really an excellent piece of software. At the moment, SpamPal is free software and the licensing restrictions could be found from http://www.spampal.org.uk/ For support and help using SpamPal, what I have learnt from using, I can help you, if you would like to contact me. But you may instead check out SpamPal forums and Contact Pages from SpamPal website. However SpamPal comes with a more descriptive and a step-by-step user manual to keep your mailbox clean and spam-free.