Old and new addresses and spam
In response to an aside wondering how fast spam fell off for disused email addresses, Henry Spencer wrote me to mention that his older address (disused now for many years) gets a lot more spam than his current address. I've been thinking about this since then and I've realized that I implicitly divide disused addresses into at least two different categories. Let us call these the old active addresses and everything else.
Put simply, the old active addresses were actively and generally widely used on the Internet in what is roughly the pre-spam era. Henry Spencer's old address is definitely one example of this, since Henry spent years being active (and famous) on Usenet. Old active addresses were visible to spammers in the era where spammers began accumulating address lists and as a result they made it on to a huge number of such lists. These lists seem to still circulate and recombine today, even though an increasing amount of the addresses are no longer valid; effectively they have an exceptionally and I suspect atypically long half-life.
(One of my old addresses seems to be like this, in fact, although not the address that prompted my earlier entry.)
Other addresses either weren't visible enough to make it on to those early spammer address lists or postdate them in general. These addresses are not so universal in spammer usage and so get hit less and, I assume, also fall out of usage faster and to a larger degree. These are the addresses where it's interesting to ask about the half life of spam. Of course what I think of as a general category here is probably some number of different ones that I don't really see because I don't have enough exposure to information about how spammers harvest and pass around addresses today.
(My impression is that one reason old active addresses are so heavily spammed is that these old addresses have become pervasively and basically freely available to spammers via many paths. I assume that newer addresses are harder and more costly for spammers to get, so they are less pervasive. This is probably an incorrect assumption.)
The real thing this has made me realize that I don't really know much about how modern spammers operate. Is there a modern equivalent of the old 'million addresses' CDs that spammers apparently used to sell and pass around a decade ago, for example? I have no idea.
(I'm not likely to find out, either, since doing so would take a bunch of work even to find reliable sources of information and I just don't care enough any more. My spam problems have been basically solved by us outsourcing the work to commercial software.)