How to Add a DMARC Record Safely
Domains & DNS · Self-help guide
DMARC tells receiving mail servers how to handle messages that fail SPF or DKIM checks. To add it safely, start with a monitoring policy rather than a strict blocking policy. Log in to your DNS provider and create a TXT record named _dmarc. A basic starter value is v=DMARC1; p=none;. This does not reject mail, but it allows you to begin using DMARC. Some businesses also add a reporting address, but only use an address that is ready to receive DMARC reports. After saving, allow DNS propagation and test the record with a DMARC checker. Do not change p=none to quarantine or reject until SPF and DKIM are correctly working.