Messaging Server has a general purpose mechanism that you can use to reject mail in accordance with a variety of criteria. This criteria includes the message source or destination email addresses, as well as source IP address. For example, you can use this mechanism to refuse mail from specific senders or entire domains (such as mail from firstname.lastname@example.org). Should you have large lists of screening information, you can extend your lists with a database that stores the access criteria. While not UBE-related, this same access control mechanism is also suitable for maintaining a database of internal users who are or are not allowed to send mail out certain channels. For example, you can restrict on a per-user basis who can or cannot send or receive Internet mail.
See Access Controls for more information.