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 in 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.