HawkOpen can only track an email to which it added its own tracking image and links before sending. That happens when you send from Gmail, Outlook on the web or Yahoo Mail with the extension switched on and signed in, from the HawkOpen dashboard, or in a campaign. An email written in another app, for example the mail app on your phone, has no tracking elements, so HawkOpen never sees it.
Tracking is off for every company until its owner or an administrator switches it on, either for every message or only for the messages and campaigns where the sender switches it on. Even then HawkOpen tracks a recipient only when a consent of that person for your company is recorded, separately for opens and for links; without it, the copy has no tracking image and no tracked links.
Then check: the extension is installed and connected; you have accepted the current contract documents (the data processing agreement and the Message Tracking Terms); the tracking switch was on for that email; the email had one recipient (for several people, send from the dashboard or a campaign so each person gets a separate email); tracking was not switched off for that message or campaign; the recipient is not excluded by your own rules and has not refused tracking.
An open is recorded only when the recipient’s mail app loads images. Some mail services load images through their own proxy; HawkOpen records those too, with a label that says so, rather than as human activity.