DMARC (Domain-based Message Authentication, Reporting, and Conformance) is a crucial email authentication protocol that helps prevent spammers from using your domain. By implementing DMARC, you can instruct recipient servers on how to handle emails that fail authentication checks (SPF and DKIM). This includes options to monitor, quarantine, or reject unauthenticated emails, effectively protecting your domain's reputation and improving email deliverability. Monitoring DMARC reports is essential for identifying legitimate sending sources and unauthorized attempts to use your domain. A gradual implementation, starting with monitoring ('p=none') and progressing to stricter policies ('p=quarantine' then 'p=reject'), is recommended to avoid blocking legitimate emails.