Hermes is an open source E-Mail tracking solution that is written in Go. It tracks emails using a tracking pixel and when it detects that the e-mail was read, it sends a notification using Gotify. This is not meant to be high-quality or easily readible. I made it three hours after learning go to practice, so don't judge me! For more info on how this works, just read the code, it is not that long anyways.