Take a look at
SpamSieve. It works with several Mac mail programs including Outlook. I haven't used it personally but it seems to be well thought of.
Because I have about a half dozen Web sites, which get harvested for my e-mail address by bots, I receive as many as 100 spam messages a day. I found the built-in anti-spam capabilities of Apple's Mail to be insufficient to deal with this. So I purchased and installed SpamSieve.
If you want to deal with spam effectively, without any risk of losing legitimate e-mails, I can't recommend SpamSieve enough:
SpamSieve ($30)
http://c-command.com/spamsieve/
Review:
http://www.macworld.com/article/301...ve-spam-filter-for-your-mac-email-client.html
Set up is extremely easy. To start off, you choose a bunch of spam e-mails in your e-mail program and mark them as spam. Then you choose a bunch of your typical non-spam e-mails and mark them as non-spam. SpamSieve automatically analyzes both samples and looks for things common to the spam that you receive, and things common to the non-spam that you receive, and it creates a series of filters to form a blacklist and a whitelist. From then on when you get a spam message in your in-box you mark it as spam, and SpamSieve adjusts it's filters. You do the same for non-spam that shows up in your Spam folder. In just a few weeks SpamSieve becomes amazingly accurate. All of my spam messages get filtered into my Spam folder like magic for me to review and trash.
See:
http://c-command.com/spamsieve/help/identifying-spam
The best thing is that since SpamSieve is adaptive, and it doesn't run off of a database that its developers created, spammers can't change their addresses or writing style to defeat SpamSieve's effectiveness.
Currently, according to SpamSieve's statistics, I'm receiving an average of 60 spam message a day, and SpamSieve has been 99.8% accurate at sorting them!
According to C-Command's Web site, it is compatible with Outlook.