I just received my first "mailing list memberships reminder" from a mailman list. I asked the list admin about it, and he replied:

Each mailman installation optionally sends a single message covering
all the mailing lists controlled by that installation, once per
month. The option is controlled by the list administrators, though;
not by the individual users. I could turn it off, but then I'd have
to turn it off for everyone.

I strongly suggest that this become a per-subscriber configurable item.

Consider the possibility that I, unaware that this is going to take place, subscribe an address that represents a local exploder. At some later time everyone on that local list is going to be given my password, possibly without my personally being aware it has happened (if I don't happen to be on the list myself).

That sort of information should never be mailed to someone who hasn't explicitly asked for it and verified in some way that he's eligible to receive it.