I'm getting email notification on discussions that I did not post to. This evening, I've received two emails on the same conversation thread. I selected the option to not follow the conversation both times.
There have been glitches with the emails coming in Jodi, I don't think you're alone. I think the best thing is to submit this to Ning with specifics (which conversations you're getting emails from), as this something that I unfortunately have no control over. Thank you for reporting it here, however.