A quick search at mxtoolbox.com shows:

Category    Host    Result  

dmarc   example.com     No DMARC Record found    More Info

spf     example.com     No SPF Record found      More Info

mx      example.com     No DMARC Record found    More Info

mx      example.com     DMARC Quarantine/Reject policy not enabled   More Info

dns     example.com     SOA Expire Value out of recommended range    More Info

for a particular domain (not "example.com" obviously).

I was seeing that to lookup DMARC records, for example, with dig the syntax is like:

dig TXT  _dmarc.example.com

But how is the existence of a DMARC record established from dig?