There are three methods of fighting SPAM.
1. Real time block lists.
This requires no third party products, but finding the right block lists can be tricky. Spamhaus, ORDB, and Spamcop are good starts. As far as I know Spamcop blocks Gmail due to some technical reason. Real time block lists are great because they block the spammer at port of entry and some worm attacks will also be tharwted with RBLs.
2. Using heurists application such as SPAMAssassin.
Well we've used it for over a year and it's ok, but not great. It will block a lot of spam. It will also give quite a few false positives. Unfortunately spammers have learned how to adapt to these kinds of apps so they're getting past them. Then again paying 49 bucks some some basic protection is a small price to pay for greater productivity gains and at least some defence against SPAM, which is generally a big pain in the arse. The difference between Plesk SPAMAssassin and 4PSA is that 4PSA have designed a great interface around SPAMAssassin and 4PSA has excellent support. But essentially it's the same product, only 4PSA's is easier to use and administer.
3. Greylisting.
This is by far the most effective way of combating SPAM. It's not perfect, and it's not built into Plesk, but installing it with the help of a Linux engineer should be a breeze and it's by far the most effective method. It also greatly reduces the load on your network and your e-mail server. It's based on a basic principle that spammers use applications to launch their attacks and these applications do not have a retry interval, whereas e-mail servers that are properly programmed always have a retry interval. What happens is your e-mail server rejects every single message on first try, returning an error code stating that the originating e-mail server should try again later. This transaction gets recorded and should the originating e-mail server try again the message will go through. I would highly recommend it. See this post for more information:
http://forum.swsoft.com/showthread.php?threadid=28645
Please bear in mind if you have a 64-bit operating system or using a Debian derivative you will have to make minor modifications to the standard install, these are all documented if you sift through the post.
Facebook
Twitter
