Domain Setup and DMARC??

Our website is a Shopify store which sends emails to our customer list and we are having serious problems with Comcast (and others) marking our emails as Spam.  Shopify suggests that we need to add a DMARC record.   

1) I don't see where to add a DMARC record (or a CNAME) and

2) There appear to be some problems with our domain setup: 

    a) Under Nameservers there are NO Name Servers listed and a message says "It appears that our partners are experiencing some technical difficulties, so we are unable to process your request at this time. Please try again later." 

    b) Under Advanced DNS Settings it says "Oops! Looks like no website builder site found for this domain , please try resetting domain by creating website."   

Help?