1) Postini and other off-site similar services
3) VAMSoft ORF
However, ORF costs way less. As of August 2011, ORF is $249 for the first year and then $99 each year thereafter. This is for unlimited users.
Also, ORF requires minimal configuration, which I'll go over here.
After installing ORF, the first change I make is to add an external DNS server. I add Google's public DNS, 126.96.36.199 as seen here:
The next thing I do is enable the tests I like. Unfortunately, before I did the installation where I took these screen shots, I didn't track which tests I enabled. It's only three or four tests, but here is a screen shot with all the tests I enabled after I had enabled them:
In the test for DNS blacklists, I enable SpamHaus Zen and SpamCop:
The last change I make is to add URL blacklists. I have it check the combined SURBL list and uribl.com blacklist.
After making those changes, click Configuration -> Save Configuration. Then go to Information -> Status Information and choose Start to start the ORF service.
Separately, I also disable any other spam filters. Almost always, I'm replacing the built in spam features in Exchange. I open Exchange Management Console and go to the various hub transport modules and disable any and all spam tests in the anti-spam tab.