Lou,
It could be an attack, but maybe not. Could just be people
taking a net class and learning how to sub to a list, then unsub.
I get that quite often. When I get a slew of new subs from the
same domain, then a slew of unsubs for the same domain I don't
even look at them anymore, I delete them just from the mail index.
However, sounds like you are sub by owner and they ought to pick
an open or open,confirm list for their practice.
Douglas