In GoDaddy: open DNS Management for your domain, Add a TXT record with Name _dmarc and value v=DMARC1; p=none; rua=mailto:[email protected], and save. Monitor reports, then change p=none to enforcement.
Sign in → My Products → your domain → DNS → Add. Type TXT, Name _dmarc, Value your DMARC string, TTL 1 hour. Save.
Leave it at p=none while you authenticate senders via the aggregate reports, then edit the record to p=quarantine and finally p=reject.
Confirm it resolves:
$ dig TXT _dmarc.yourdomain.com +shortCheck your DMARC record now
Open the free DMARC checker →Use _dmarc — GoDaddy appends your domain automatically.