But the problem with relying on tracking pixels to flag whether a message is read is that not everyone loads them. I've had my mail clients (and Gmail) set for

But the problem with relying on tracking pixels to flag whether a message is read is that not everyone loads them. I've had my mail clients (and Gmail) set for years to not load external images, and occasionally get "we notice you haven't been reading our messages so we're going to stop sending them to you" emails from mailing lists that I do actually read.