DNS blackholing blocks access to known malicious infrastructure by resolving selected domains (or related lookups) to a non-routable or controlled sink address, effectively preventing systems from reaching attacker-controlled destinations. The question specifies blocking malicious sending infrastructure “at the DNS level,” which directly points to DNS blackholing. While firewall IP blacklisting blocks network traffic by destination IP, it is not DNS-level control and can miss cases where infrastructure changes IPs frequently or where domains are the stable pivot. URL blacklisting on proxies is a web control and may not cover non-web protocols used by malware or email infrastructure. SMTP filtering focuses on email transport controls at the mail server/gateway level and is effective for blocking inbound spam, but it is not DNS-level blocking. In SOC eradication, DNS-level controls are often used as a fast, scalable mitigation because many malicious workflows depend on name resolution (phishing landing pages, malware C2, payload hosting). DNS blackholing can also provide detection value by logging attempted lookups to known-bad domains, helping scope affected hosts and validate whether users or systems are still attempting to contact attacker infrastructure.