I am receiving messages that ITB users are getting the automated email to advise that they have ITB messages in their inbox and when they check there are no new messages.
You can disable this automated email by selecting "my account" "edit" scroll down page to "Private message settings" and uncheck the box for the automatic notification.
ps. As pointed out in a comment, and I can confirm this, a number of users are registered with more than one user name on the same email address and this would account for the automated message if you are not checking the other user name(s) inbox. If you wish duplicated accounts to be deleted, please advise me.
Admin2