Someone registered for my site, and promptly posted spam in a Forum.  I went in and deleted the user, but now, when I try to delete the thread, it throws an error, apparently because the notification email failed.  If I try to re-create the username, I'm told it still exists, despite not appearing in the  list of accounts.  Obviously, I should have deleted the thread before the user, but what's done is done.

I can't find any control over the notification process.

The user name does not show up under User Accounts.  If you click on the user's name in the Forum Post, you can get to a User Profile page that shows his UserID, and you can click on Manage User, and get to a User Profile page, but the page doesn't offer any choices besides Cancel and Update.  It looks like you might be able to change the USerID here, but I hesitate doing that without knowing the consequences. You can't search by UserID in User Accounts.  I posted this to Forums since preventing the delete thread notice email would fix the problem.