⟩ How do I restrict a user or domain from sending mail to my users?
First, add the address or domain you wish to filter to the Filtering Tab of the Message Delivery Global Settings. Next, you need to apply the filter to the SMTP virtual server you wish to filter. (Administrative Group | Server | Protocols | SMTP | <SMTP Virtual Server> | Properties | Advanced | <select the IP address for which you wish to enable filtering> | Edit | Apply Filter). Normally, you would only want to apply message filtering to the border SMTP servers (servers that communicate directly with External servers).
