I have no idea either. I track every email I send out. The issue with tracking, when done by companies, is what they use that data for. People don't want to have sales profiles built on them or have their literal privacy - in terms of their personal web traffic - being invisibly tracked and potentially exploited by bad actors.

On a personal level, I send emails for a variety of reasons, and I haven't found a good reason why I wouldn't want to know when they were accessed.

1. I've sent legal correspondence and it's important for me to have a record of when and how frequently it was accessed in case it ever reached court.

2. When I send emails to my staff, I'm less interested in whether or not they reply and more interested in whether or not they read the emails at all. If not, then I can use alternative and more immediate forms of communication.

3. Sometimes I'm ignored by people that owe me money for one reason or another (in one particular case, I was almost scammed out of $40,000). Knowing that the correspondence I was sending was being accessed but was being ignored allowed me to take more immediate action.

I'm not building profiles on people, I'm not trying to sell anything. And I'm not going to apologise for it either. My intentions are not malicious, so that's where it starts and stops for me.