>It's so annoying if mail is accepted but you don't know if it is actually seen by the recipient.
that's what those embedded 1x1px images are for
that's what those embedded 1x1px images are for
There is also no guarantee that the image being loaded means that the user opened the mail and it wasn't just preemptively cached by the server/client. There is also no guarantee that the user opening the mail means they read it.
I'm not here to guarantee anything, just mentioning the technology exists and is still widely employed. there are no guarantees with messaging app ticks either