[vk6flab]

The headers actually contain an unsubscribe email address that actually works.

The format is something like googlegroups-manage+{groupName}[e-mail]

Just send an email there and they stop coming (for that list).

Source: I was getting spam like this, a fellow victim did some tests and confirmed that it stopped the onslaught of messages.

[avian]

I just block the group address on the MTA, but it doesn't matter. In all instances so far when it came to my attention the group was already deleted. Next time they will use a different group and I don't want to blanket ban all Google Group mail for my users.

It's not even that much of a hassle. What worries me is that I don't understand why someone would go through the trouble of doing this for no apparent benefit. I hope I'm not somehow unknowingly enabling some sort of an attack on any of the entities sending these automated replies.