FBL stands for feedback loop, a system that some large email providers (mainly aol, yahoo and msn, but not Google) have set up so that we can receive reports when their members mark emails as spam. The assumption is that we will unsubscribe these people.
The way we deal with these reports is the same as when someone clicks an unsubscribe link in a message footer. We unsubscribe them, and send a notice to them with a resubscribe link that's valid for 3 days.
I turned the system completely off last year because I was receiving reports from people who were being unsubscribed but claimed that they weren't marking emails as spam. I have no direct interactions with people involved in email at AOL/Yahoo/MSN, but I fear that us not acting on these reports may be the cause of delivery issues with these companies. It appears that AOL is partially blocking us right now, for example, even though they list us as having a good reputation.
I looked at the logs for FBL reports from AOL users. Over the past day, for one AOL user, we received 166 FBL reports.
So I've turned FBL processing back on for AOL users. And at some point I'll turn it on for the others.
Please let me know if you hear from members who have been unsubscribed this way who claim they have not marked any messages as spam. One question to ask them is to look in their spam folders to see if any messages from us are in there inadvertently. Also, I'm open to suggestions for ways to improve this system.