Can a domain score 0%? Yes. A domain that is not registered, has no DNS records, and no SSL certificate would score 0%, regardless of the attack type. In practice, unregistered domains will always have at least some score contribution from their attack type if the domain status is "Parked" or "Registered."
Why does the MX record carry the most weight within DNS? MX records indicate that a domain is configured to handle email. Since lookalike domains are most commonly used for email-based phishing, the ability to send and receive mail is the strongest infrastructure signal of potential abuse.
Does the score update over time? Yes, if there are updates to the lookalike domain, for example if it was previous not registered and recently got acquired with changes to the DNS infrastructure or SSL, the score will update
How are results sorted? By default, results are sorted by risk score from highest to lowest so that the most urgent threats appear at the top.