Tracking non-Mautic emails

I’d like to be able to track emails sent by a different platform within Mautic.

I figured this would be similar to the GMail Chrome Extension since those emails would also not be sent from within Mautic but after pulling the code apart I still couldn’t figure out how it was logging the email with Mautic and handling the tracking.

When I send an email I’d like to do an API call then inject the tracking code in to the email. It should be pretty simple.
Are there any examples or documentation for this?