When work got me a cell phone, the number assigned had previously belonged to a woman who had neglected to tell many people that her number changed. So I got lots of calls and texts for her.
I finally found her by searching Facebook for the phone number, and sent her a message. Ended up having to spend the $1 to get the message to her actual inbox, but she was very nice, and grateful to know so many people didn't know about her name change.
So I say go ahead and try to track them down - perhaps a Google or Facebook search for them? If you find them, just politely let them know that you've been getting their email, including some potentially confidential personal information, and you thought they should know so they can get it sorted out. I'm sure they're wondering where their email is.
Feel free to just unsubscribe from the newsletters, since they can just sign up again, and if you can't find the person (or they don't respond) just respond to all other senders with "I am sorry, but this address belongs to someone else entirely."