So I’ve been having this realy strange problem. I use OS X’s Mail app along with SpamSieve for spam filtering. But recently I’ve been noticing that the spam detection has been hyperactive: way too any false positives. I tried re-training SpamSieve. No help. So then I shut it down altogether: Whoa! I was *still* getting messages sent to the spam folder. Next, all the usual steps: rebooting, re-initializing this and that. Still no help. With absolutely no spam filtering turned on, stuff was still being flagged and moved. (Any of you email geeks starting to get a clue here?)
For a totally separate reason I pulled out my MacBook Pro, and that’s when it hit me. I even caught the nasty gremlin in the act. What was it?
I use Google as my inbound and outbound email server. Yes, I use their spam filtering, too — it’s much better than SpamSieve — but that wasn’t it. Because I have three different email clients (if you count the iPhone) I use IMAP4 instead of POP3 to communicate between those clients and the Google server and keep things in sync. So here’s what was happening: My MacBook Pro had been on and running it’s own instances of Mail and SpamSieve. Messages would come into Google and, in some cases, my laptop would grab them. The copy of SpamSieve on that computer decided some of them were spam and would move them to the spam folder. And because I’m using IMAP4, this change was sent to the server and then to the email client running on the desktop. It was my laptop, running this other instance of my spam filtering software that was moving messages around on the email server and hence on my desktop client. It was downright spooky to see the messages moving without a clue as to why, but as soon as I realized my laptop was also running email, it became instantly clear.