[jrodom]

Josh/CTO of Mailgun here - I took a look at this case and these messages were being sent from the sandbox feature of our service. The sandbox only allows messages to be sent to "authorized recipients" through an opt-in mechanism, which makes it impractical for spamming and phishing. The purpose of this feature is to allow customers to get comfortable with the interfaces and test the product in a safe way without having to add DKIM/SPF records. I reviewed these messages and confirmed there is no illicit behavior, likely just a misconfiguration from a user of radiotoolbox.