If you're prompted to enter a code when you try to send a message using Web-Based Email, it's likely because you triggered a protective measure we set up against spammers. We regret if this caused any inconvenience.
These codes, called CAPTCHAs, are series of numbers and letters partially obscured by shapes and colors. Once you correctly enter those numbers and letters, you can continue working with the application. The reasoning behind CAPTCHA is that a real person would easily be able to enter the code, while a program set up to send spam will not.
For the Wikipedia article about CAPTCHA, go here.