PSA: GitHub Pages IP addresses have been updated
tl;dr: New IP Addresses for your DNS are now: 220.127.116.11 and 18.104.22.168
Fastly error: unknown domain: www.example.com. Please check that this domain has been added to a service.
If you’re seeing this error message as of August 22nd, 2016 on a previously working GitHub Pages domain, you need to update the IP Addresses according to this article: https://help.github.com/articles/setting-up-an-apex-domain/