I “upgraded” from Spamassassin 3.17 to 3.18 on Monday afternoon. Reading the message boards, I saw that Spamassassin 3.18 has been letting through a lot of spam for some people that upgraded, so I’ve reinstalled Spamassassin 3.17 and it appears to be filtering spam again.
I also changed the rbl xbl-sbl.spamhaus.org to zen.spamhaus.org. I came into work this morning, and there’s been no spam in my mailbox since I made those changes!