This toot was clearly from Tuta and is an info-mercal but it does contain a significant amount of useful information for general use.
TL;DR
most bigCorp email contain an image that is very small, 1x1 pixel.
When you open the email your email manager will request the image and at that point the #bigCorp knows where you are and you are giving them information to identify you in the future.
TL;DR
most bigCorp email contain an image that is very small, 1x1 pixel.
When you open the email your email manager will request the image and at that point the #bigCorp knows where you are and you are giving them information to identify you in the future.
