There could be a few reasons on why the emails arent tracked.
Could be that the add-in wasn't open when the email was sent. The add-in must be open in order for the email to be tracked. Learn how to pin the add-in open in your inbox, or to open the add-in:
When using an Outlook on the web or Outlook.com account, compose a new email and click the HubSpot sprocket iconsprocket in the bottom right-hand corner of the email composition window.
Lets start with the 365 Outlook on the Web. I've downloaded and installed the extension but the Hubspot icon never appears anywhere to be able to choose track and log