I want to test our employees to see if they will click on a suspicious email attachment. I will send it to them from a "throwaway" gmail account, with a pdf attachment and some kind of explanation that they need to open it to read instructions on delivering a package or something to that effect. I want to know who actually opens it so that I can do more training for them on security awareness. We use Office/outlook 365 for email. How can I tell whether or not a recipient opened the attachment?