If your messaging installation uses virtual domains, in which a single server instance is associated with multiple IP addresses and domain names, you can control access to each virtual domain through a combination of Allow and Deny filters. For example, you can use Allow filters like:
ALL@msgServer.siroe1.com: @.siroe1.com ALL@msgServer.siroe2.com: @.siroe2.com ...
coupled with a Deny filter like:
Each Allow filter permits only hosts within domainN to connect to the service whose IP address corresponds to msgServer.siroeN.com. All other connections are denied.