Mailtrack doesn't track emails you send to yourself, that is, emails where the sender and the recipient are the same address. The email is sent normally, but Mailtrack shows a warning that tracking is off for that email.
In your inbox, the email shows grey checkmarks. Hover over them to see Email not tracked.
How to test that Mailtrack works
To check that Mailtrack is installed correctly, send a tracked email to a different address, for example a personal account or a coworker's address. If the email still isn't tracked, follow these troubleshooting steps.
What about opening emails you sent to someone else?
When you open an email you sent to someone else, Mailtrack doesn't count it as an open, as long as you view it in a browser with the Mailtrack extension or in the Mailtrack app. On other devices or apps (for example the Gmail app on your phone), your open can be recorded as the recipient's. More details: Why does Mailtrack sometimes count my own opening of a reply as the recipient's open?