The article provides some relevant considerations when performing a regular phishing exercise. Usually, going the route with sendgrid already solves a lot of problems. For the DNS consideration, the article includes some good general pointers. SPF, DKIM and DMARC are the baseline there, but not the end of the story: Chen, Paxson and Jiang described 18 ways to make mail servers and clients disagree about who sent a message, and all 10 providers and 19 clients they tested were vulnerable to some of them.
