Mailshell has announced that its breakthrough spam-prevention and e-mail management service (http://www.mailshell.com) added its 500,000th registered user, more than 400,000 of whom have registered since January of this year. The company also unveiled a suite of premium features that simplifies and manages e-mail while preventing junk e-mail and spam. Mailshell lets users create a custom e-mail domain (e.g., @username.com) and then use it to create unlimited, disposable e-mail addresses. If any address begins receiving unwanted e-mail, the user simply cancels that disposable address. Mailshell forwards e-mail sent to the custom domain to the users' existing e-mail account, allowing users to keep their current e-mail address.