A user or domain that is assigned a quota of -1 can use an unlimited amount of your accounts global quota, meaning that there is no restriction to the size of the mailbox either for that user or for the total for that domain.
To view your current quota, login to myCP and click the Email Admin link for the domain/account in question. On the following page you will find a list of the domain (or domains) associated with the chosen account, and to the right of the domain name, the total amount of space that specific domain is using, as well as what the quota is currently. For more detailed information about the usage of a given domain or user account, click on the link for the domain itself or the "Users" link, where you can then select an individual user to see the same information.
