By default, new Web sites that you set up without the help of domain templates, are allowed to consume unlimited amounts of bandwidth (data transfer) and disk space.
To limit the amount of resources a site can consume:
Note: The overuse policy does not apply to the limits set on size of mailboxes (mailbox quota). Therefore, even if you enable overuse, be sure to allocate enough disk space to mailboxes.
To protect your site from DoS attacks and to ensure that your site responds promptly when there are many visitors, you can limit the number of simultaneous connections to the site and limit the amount of bandwidth that visitors to the site can consume: