A member reports that this week he’s received several emails fromHave him look in the message footer, next to the Unsubscribe link. That shows the email address to which that message was sent.
If it shows his address, then most likely he is subscribed to the group in question, because this can't happen by any kind of forwarding or misdirection of the message.
If it shows an unknown address then a detailed look at the message's header fields (specifically the chain of Received and maybe X-Received fields) may reveal how the message ended up in his Inbox.
Is there a systemic bug going on here?Maybe. There were a bunch of reports in GMF of AOL users receiving misdirected groups.io messages, not recently though.