How tracking pixels work

[nelsonic]

https://jvns.ca/blog/how-tracking-pixels-work/
https://news.ycombinator.com/item?id=21832112

[nelsonic]

Implemented this in:
https://github.com/dwyl/email/blob/b4c2c4f4d96773c326cf3fa8cd4838973c9a78f5/lib/app_web/controllers/sent_controller.ex#L113-L147

Still worth adding the link to the "Recommended Reading" section. 📝