YAZSOFT SUPPORT  I get very stressed out and paranoid when I'm checking my email on a machine with out SpamSieve. This utility is a true blessing and one powerful spam-buster!!! Never check email without it.  
(Version 2.7.3)

MISHA  I've been using SpamSieve for years—it's the best solution out there for Mac users, and Michael keeps improving it.

I only wish that it was easier to transfer configurations and corpuses to other Macs. Right now it's a fairly tedious process of copying a few different things over (Preferences, Application Support, the app itself, and any scripts that you have changed). .Mac syncing or something similar would rock!  
(Version 2.7.3)

ZIGGY29  SpamSieve is the best consumer-grade, easy-to-use spam filter I've ever used, bar none. I've done system/network administration on Unix, Mac and Windows systems, and for the end-user there is simply not a better spam filter I've ever seen. Once trained, it catches well over 99% of the spam and virtually never records a false positive.

I've compared the spam filters in both Apple Mail and Microsoft Entourage, and while both of those are competent (though sometimes lacking), SpamSieve just gets better and better at identifying and quarantining spam as you use it more.

At the $20 price point it would be even more compelling. But for those of us who would get dozens of spams day after day, every day, the $30 price point is still worthwhile in terms of reduced aggravation and lost productivity dealing with massive waves of junk e-mail.   
(Version 2.7.2)

RODPAINE  As others here have expressed, this little application does an excellent job of snagging SPAM and its learning feature works very well. I am using it with an older version of Eudora Pro under OS X 10.4.11 and it has served me well for a long time.

FWIW,

-Rod  
(Version 2.7.2)

UETLI  excellent Spamfilter.  
(Version 2.7.1)

SILVASURFER  As a registered user I have been using this app now for close to 18 months and nothing comes close to it for spam catching & protection. No it won't solve all your spam issues (what does?) but it is the best mac program out there. Recommend to all my friends who have switched and or bought new macs and they are very impressed. Constantly update, good documentation and a responsive developer.

A must have app for you Mac!  
(Version 2.7.1)

FRYE  I've been using this for a while with Entourage, and as others have said, it is simply the best protection you can find for your inbox. Between my service provider stopping spam at the source (so I never have to see it) and SS stopping the ones that trickle through, it is truly a time-saver. Like many people I have different email accounts for different purposes, so spam can and does get unruly. SS is the only solution I've found that makes a difference.

While it is difficult to set up (you definitely need the help guide), once done it basically runs on its own. I think the price is a little steep, and would recommend the developer charge $19.99, but I can also understand wanting to get compensated for the blood and sweat that went into creating the application. I think at a lower price point, they could sell even more copies, which in turn will take an even larger bite out of the spam inundating inboxes everywhere.  
(Version 2.7)

EDMUND51  Found this application via a google search.

I just convert from PC to mac and had a similar product.

I can't tell you how much well it works.

I have multiple web pages that had my email address listed on them. On any given day I receive somewhere around 500 emails only 30 or so are not spam.

After I installed SpamSieve 99.99% of the junk goes in the spam box.  
(Version 2.6.6)

F451  I have so tried so many of these applications throughout the years, but SpamSieve is the definitive spam filter application. Excellent support, and application.  
(Version 2.6.6)

GARY30  I used to use SpamSieve and it is a great product worth 5 stars. I have a public email address on my website and various other email boxes that go back to 1994. So SpamSieve has been essential.

However, recently I had to go out of town for an extended period of time and wanted to be able to access all my email from a single service with a web interface if needed. I selected gmail and arranged to forward all my email accounts (except for a free yahoo account) to the gmail account. Result: Zero spam and complete transparency as far as the senders are aware. I could have literally not told anyone I was gone and could have received and replied to all email using the original "Sent To" addresses for my replies.

Not that there is anything wrong with SpamSieve, but one less program to run is one less to deal with and upgrade. So far, gmail has a perfect spam rejection/wanted email acceptance record.  
(Version 2.6.6)