This was not just a matter of people getting forwarded messages with misleading headers, since most of these people were in fact on the mailing list. Finally this week I sent a query on the subject to the whole list. Here is a summary of what I learned. The Internet has indeed been suffering an epidemic of bogus mailing list subscriptions, particularly over the last few weeks. I have had reports from numerous list maintainers of dozens of mysterious subscriptions suddenly showing up on their lists, followed by confusion or acrimony.
Some instances are clearly malicious.
Numerous people have been involuntarily subscribed to many mailing lists. List-bombing, however, does not seem to be the only phenomenon here. Only a few of the people who complained to me mentioned other mailing lists, and I think that victims of list-bombing are much more likely to change to a new account than to try unwinding all of their bogus subscriptions. On my list I speculated that a demon might be generating subscriptions on a random basis, but nobody has reported any actual evidence for this. At the same time, it seems to be happening on too large a scale to have been done entirely by hand.