For reasons beyond the scope of this entry, I've started running a little 'sinkhole' SMTP server to collect email for what is essentially a disused set of old addresses of mine. The server takes in everything, logs the messages to disk, and then tells the senders that they weren't delivered; later, I can go through the logged messages to see if anything interesting has shown up. In the process of doing this I've noticed that a surprising amount of the spam comes with List-Unsubscribe headers with URLs. So I've been using some of them to see what happens (especially when I recognize the sender as a long term repeat offender).

Normally it's an article of faith that you should never, ever use a spammer's unsubscribe procedure. Doing so only confirms that your address is live and perhaps helps the spammer, reducing the load on their systems and so on. I'm not sure that what I'm doing here is exactly sensible (although it makes for an interesting experiment), but I don't think it's completely crazy.

The big difference between my situation and the normal situation is that the addresses I am 'unsubscribing' are already dead addresses as far as I'm concerned. They basically no longer get valid email (and some of them don't even exist) so any increase in the amount of spam coming to them is immaterial; it's just more grist for the sinkhole to reject. Also, these addresses have been aggressively defended for what is now years and spammers have been trying to bang away at them for years. It's clear that the repeat spammers I can recognize simply don't notice or don't care about any extra load on their mail sending systems that I've been creating with prior tactics like blackholing SMTP traffic from their IPs in the firewall. If they did they would have removed such unresponsive addresses by now, often years ago.

At one level I don't care about the load on my sinkhole, but at another level I do. I'm running the sinkhole to collect interesting new things, and yet more spam from some usual suspect is completely uninteresting. If I can make it go away by unsubscribing rather than making the sinkhole's environment more complicated, so much the better for my real goals.

Or at least that's my thinking so far. I may change my mind later and stop doing this.

(But I'd also find it very interesting if unsubscribing actually seemed to increase the spam from the usual suspects, or even increased it. Seeing if this will happen is one reason I'm bothering with the experiment at all.)