The Contest Commissioner can easily contact the full list of Players by grabbing the Player Email List.
This activity is done from the Players Settings Page, from within your Contest Settings.
Please note that the Email List will only contain emails from Players who joined the Contest themselves. Any "Offline Players" that were added by the Commissioner do not have real SBPS User Accounts behind them, so they therefore do not have stored email addresses within SBPS.
Below the Squares View, you'll find a directory listing of each owned box in your Contest.
The Full Email List of All Players
In the top-right corner of that section, click on the "Player Email List" button. This will bring up a full, unique listing of all Player Emails in your Contest.
The lists are provided with a comma separated version, as well as a "one per line" version, which can be easily copied and pasted into the spreadsheet or mail program of your choice.
A Single Player's Email Address
If you are just looking for the contact email address for a single player, you can locate that Player in the Listing View directory and click the "Email" button found on that record. The popup window will give you the details for that Player, including their email address.