• Log in your cPanel and go to Advanced DNS Zone Editor.
• Add a new TXT record with the following details:
  • Name: _dmarc
  • TTL: 14400
  • Address: The text depends on the way you want servers to handle your emails:
    • none – Take no action. Log affected messages on the daily report only.
      v=DMARC1; p=none; sp=none; rf=afrf; pct=100; ri=86400
    • none with report – sends report of failed validations to a valid email of yours (example: admin@domain.com)
      v=DMARC1; p=none; sp=none; ruf=mailto:admin@domain.com; rf=afrf; pct=100; ri=86400
    • reject – Cancel the messages
      v=DMARC1; p=reject; sp=none; rf=afrf; pct=100; ri=86400
    • quarantine – mark messages as spam
      v=DMARC1; p=quarantine; sp=none; rf=afrf; pct=100; ri=86400

Please allow several hours for propagation. If you wish to double-check the validity of the added record, you can do that on this website:
https://dmarcian.com/dmarc-inspector/