Mark,
I suggest implementing SpamFoo in one of two ways:
If you're already using Cyren and MessageSniffer, add SpamFoo with a weight of 5. This gives it an extra push for messages that are already trending toward spam based on your existing antispam scores. Once you're satisfied with the results and decide to remove Cyren and/or MessageSniffer, simply increase SpamFoo's weight accordingly.
If you're not using Cyren or MessageSniffer, assign SpamFoo a weight of 15 and let SmarterMail's built-in antispam features provide the additional scoring needed to classify messages as spam.
A combination of Greylisting, DKIM, SPF, RBLs, and URIBLs is extremely beneficial as part of an overall antispam strategy when used alongside SpamFoo—or any other third-party antispam solution. Assigning many of these a score of 5 helps push messages that SpamFoo already suspects are spam over the threshold for spam.
I'm using our default scoring weights as examples, while recognizing that many of you have heavily customized your scoring or use a completely different scoring model for your environment.
As users move messages between categories—or into and out of Spam—their mailbox becomes increasingly refined, eventually reaching the point where it consistently understands how they want their messages classified. This feedback is also passed upstream to the server and our models, helping further improve how messages are categorized as Spam, Not Spam, Promotions, Transactions, Primary, and more.
Any changes to your antispam configuration—including the features built into SmarterMail—should be made slowly and evaluated over time.
In the near future, some of the traditional antispam features in SmarterMail may no longer be necessary. Internally, we're already beginning to disable some of these settings and rely more heavily on SpamFoo because it's effectively operating as though a human were reviewing every email.