Where does this "[POSSIBLE SPAM]" tag come from?

Occasionally (probably about once a day), I get an email with [POSSIBLE SPAM] prepended to the subject. It only happens in my Optimum Online inbox (doesn’t happen with either Gmail or Yahoo! Mail), and is rarely (if ever) spam.

Is there an ISP-level spam filtering package that does this? I got no useful info out of the Optimum Online folks.

ISP-level anti-spam software can do that, yes. I have accounts through different providers. One has software that tags questionable items as [Spam?] or [SPAM] or [Phish-warning], etc. The tags and the settings for what triggers them can be modified by the ISP, as well as some of the settings. For example I get some mail through a friend’s mail server, and it was for a while tagging everything sent from MySpace as [Spam?]. I told him it wasn’t, really (though the frequency of some of the emails would make it look like it) and he added MySpace’s IP address to the list that didn’t trip the spam filter.

Email also isn’t direct delivery: It makes hops between any number of mail-forwarding computers between the source in destination. It’s conceivable one of the machines en route could do that as well so that it wouldn’t necessarily have to be at your ISP, but I’m not sure on that. Machines in the middle probably don’t want to waste too much time analyzing content of mail going through just to save processing power.

I think the point is that Optimum delivers you all your email, but if you want to take advantage of the spam filtering feature you can just set up a simple rule in Outlook.

Well, yeah, but I just wanted to figure out where it was coming from, since it’s not appropriately tagging spam (or, rather, it’s inappropriately tagging non-spam). At this point, I’ll have to assume it’s from OOL, but since there’s no way to disable the tagging (at least not in my user configuration screens on OOL’s website) I guess I’ll have to live with it until I switch everything over to gmail.