Access Control Lists are used to explicitly define senders and receivers that are allowed to send and receive on your email system. ACL's can be used for address verification or to limit a group of users to only receive email form certain users, or allow some users to send to the Internet and others to only send internally. Access control lists are optionally integrated with LDAP so that you can query remote user diretories for address verification. We support LDAP cacheing for scalability and different LDAP configurations per policy-group, which makes us ideal for service providers who must validate addresses against multiple customers user-directories

ACL's are pre-queue for Postfix and post-queue for all other email servers.