@c_m78 Semantics. ^_~
If one is using the web interface of their email provider, then that is their “email client”.
Regardless, the point here is that they are tracking their newsletter subscribers by tracking if they're opening the newsletter they're sending. Which is, well, no one should do.
I agree, it could be that their tracker is not working, at least if it was sent by some other newsletter. Though in this particular case, I think it's safe to assume that they do know what they're doing. Hehe.
^_^