Secure Access by IP Address, Subnet, or Domain
To further enhance security, you can selectively grant or deny single computers, subnets, and entire domains access to an IMAP4 virtual server. By default, all computers have access until you add them to a list of restricted computers. However, you can restrict access to the IMAP4 virtual server by listing only a few computers, or by specifying computers that do not require the service. This feature is very useful if you create multiple instances of an IMAP4 virtual server. For example, by restricting a client's access to one IMAP4 server but allowing access to another, you can ensure that the client logs on to only the server it is configured for.
To secure access by IP address, subnet, or domain: