For those of you that feel the need for Bayesian filtering and don't want the expense of Cyren or MessageSniffer (which do much of the same thing on their own systems) there is an alternative that is much lower cost. You can use SpamAssassin In A Box by JAM Software to configure a fully operational version of SpamAssassin that works great with SmarterMail. It does take some time to get the configuration right, but once that's done it can take over most or all of the spam filtering for you (and includes Bayesian filtering). It only cost about $50 per year.
I used SpamAssassin In A Box for several years and had good luck with it. I personally dropped it when I switched to MessageSniffer. I had our inbound spam filtering as good with SpamAssassin In A Box as we get with MessageSniffer, but SpamAssassin is not the way to go for outbound filtering. MessageSniffer is excellent for outbound filtering as well.
The ONE good tool that SmarterTools gives us for outbound protection (Abuse Protection - Bounces Indicate Spammer) hasn't worked for years. If that one tool worked it would essentially solve a huge problem, but I have to face reality that they'll never fix it.
The point is that there is a choice.
I don't want to go off topic, but there was a comment that SM17 is going to use a different setup for DNS. I have no idea why SM is in the DNS caching or any third party service for any reason. We ALL run SM on a Windows server and every Windows server has a very fast an accurate DNS server built in... free of charge. Most URIBL's and some RBL rate limit or block public or high volume DNS query servers. I don't know of any reason any SM installation should use anything but the DNS server on the local machine. There is no value of any kind for using a public or third party DNS resolver.