Set up DMARC
How to Set up a DMARC Record
DMARC records are set up in the domain's DNS (Domain Name Server). When you set up your DMARC record you choose the policy type (reject, quarantine, none). - we recommend setting to none initially, then after monitoring the abuse reports, change to quarantine or reject as necessary. This record tells the server what should happen to messages that fail SPF/DKIM checks.
The following online tools may help you: