Its not for a any particular report, its for the announcements that are generated by the Tableau development team like when they are making changes to servers.
We managed to find this page for managing subscriptions like this:
It sends us an email, then we clicked the link from the email and it shows various subscriptions choices (we are signed up for all of them). However there isn't one for "Maintenance & System Communications" which is the one we unsubscribed from. Do you know where that one would be?
Doh! Apologies Chris.
If you've got an example of the email you're referring to, then I suggest you forward it to email@example.com and explain your problem. Hopefully they can track down the relevant internal department and get you sorted!