Once in a while I get users who don't fill out their email address in their Account Settings. This only becomes a hassle when a Publisher does it, however, as a just-in-case I like EVERYONE to have their email address entry filled in. As a periodic check I created a simple, live connection report to show me who is in violation.
While the attached workbook is only for one data source you can very easily modify it so it will look at all of your environments like what I did (first tab is PROD, second tab is QA).
Workbook is version 9.2.4. You will need to edit the connection so it points to your Tableau Server and you need to have the "readonly" account enabled.
Unused fields are hidden so if you are looking for more info on your Users then be sure to Show Hidden Fields.