Final answer:
To prevent communications with untrusted email addresses and domains, users should use system address filters by setting up rules to block or flag these emails. This enhances email security and blocks unwanted emails automatically.
Step-by-step explanation:
To prevent a system from communicating with untrusted email addresses and domains, a user can employ system address filters. This feature allows users to create rules that automatically block or flag emails from specific addresses or domains that are deemed untrustworthy. By setting up these filters, the system can prevent unwanted communication and enhance email security. The correct choice from the given options would be (a) System address filters.
System address filters are typically found in email management programs or security software and can be customized according to the user's preferences. Users can add known spammers or suspicious domains to the blocklist, ensuring these communications are barred from reaching the inbox. Furthermore, many email services also provide the option to mark emails as spam, which helps the email system better identify and filter out similar messages in the future.
Other options mentioned, such as system restrictions, could refer to a broader set of controls within the operating system or applications that govern user capabilities. Platform security is a general term that encompasses all security features to protect a computing platform. Suspicious activity finder isn't a standard term for an email security feature but could refer to tools or algorithms designed to detect and alert users to potential security threats.