These are the IP addresses and domain names from which Duo Insight sends its phishing emails. You may need to configure your mail provider to allow emails from these IPs and domains if you find that incoming emails are being flagged as spam.
Phishing emails from Duo Insight will contain a custom email header. If your mail provider supports it, whitelist emails that have the
X-PHISHTEST header with the value
Below are links to documentation for several common mail providers on how to configure whitelisting.