If your IMail user database is a Windows NT Database, IMail Server creates a user mail account for each user listed in the Windows NT Database. The user mail accounts are created, as necessary, when the mail server receives a message addressed to the user or when a user accesses the IMail Server from a mail client . You cannot add or delete users using IMail Server Administrator; instead, you need to use the Windows NT User Manager. If you are using Active Directory, you need to set IIS to use a domain user.
To configure IMail Administrator virtual directory for anonymous access in IIS: