While not always strictly mandated, DMARC (Domain-based Message Authentication, Reporting & Conformance) is becoming increasingly crucial for email deliverability, brand protection, and compliance with evolving requirements from major mailbox providers like Yahoo and Gmail. Mailgun strongly recommends DMARC, and Yahoo requires SPF or DKIM authentication, recommending DMARC. Google mandates DMARC for senders sending over 5,000 emails a day. DMARC protects against spoofing, phishing, and unauthorized use of domains, and major providers use it to filter spam, making it effectively a requirement for many senders, especially those sending bulk emails.