What are DMARC records and how do they relate to Cloudflare Email Relay Access Denied?

DMARC builds upon SPF and DKIM. It instructs receiving mail servers on how to handle emails that fail SPF and DKIM checks. A DMARC record tells the receiving server whether to accept, reject, or quarantine emails that don't pass authentication. Proper DMARC implementation is vital for preventing email spoofing and improving deliverability, and a misconfigured DMARC can cause Access Denied errors.