@ pipelayer: The easiest solution is to clear some space out of your PM box. Remember that sent items might be stored, as well as ones you've received.
Near the top of the page, directly below the Ottawa and Mississauga escorts links, you'll see a link called Forum Actions. Click on the downward pointing arrow directly to the right, and click on General Settings. Scroll down a little bit in the settings page until you find the Messaging & Notification section. Most likely, the box is checked for "Receive Email from Administrators", which is enabled by default, and you should keep that setting. Farther down, there's a button enabled or disabled for "Email notification of Private Messages"; you may wish to change your current setting.
The Email you got would have been sent automatically when your stored messages approached 30. It's very likely that other members receive the same one every day.