If you get this in your mail logs and the email gets bounce, ths issue is quite simply, but eluded me to start with. Also I found odd how it suddenly started happening when my postfix server had been running fine for years without this. Odd
SOLUTION: add this domain to mydestinations. I thought it was, but noticed it was a sub-domain (local name of mail server on my LAN, a subdomain of dward.us). So added it in full, restarted postfix and voila! Fixed. Mail to root now goes through fine.