Account Activation Email Spam

I recently added several users to our clubs website 8332.toastmastersclubs.org/ .
Most approved their automatic email request just fine but one began to spam our officers repeatedly with account activation success notifications.
We are a mostly corporate club so I don't believe emails from that domain have been a problem in the past.
"<user name> Approved their Addition to ToasTRS Website".
The emails arrive 3 to 4 times a day. Sent in the afternoon.
I am trying to resolve if this is happening on the users email client side.
I was curious if there is a way to tell if this is happening on our website side.

Without the name person who you think is causing the issue there is nothing we can do.