We often set up staging sites for clients, and deploy all enhancements to that staging site first so that the client has an opportunity to test and validate new features before they go live. These staging sites occasionally contain production data to make testing easier and more realistic, which also means that even real user e-mail addresses can make their way to it. This potentially implies the risk of sending out unwanted e-mails to those addresses.
A blog about web development and Drupal.