I am interested in this from a development stance, and wonder if there is any way around however it works. I have no interest in installing this myself. Does this work just for web-based clients, or does it also work if the "target" is using, say, Outlook on their computer and their email address is not some gmail or yahoo account, but a corporate account (like on an in-house Exchange server)? I think it probably doesn't matter, but I don't know. Very disturbing since this seems to expose a massive privacy vulnerability in how email is relayed. I definitely do agree with the people who have expressed privacy concerns. The most disturbing thing to me is that most people don't know that this information is accessible, and therefore can't make informed decisions based on that knowledge.

But I also don't judge you, OP. And I'm sorry this is causing you so much distress. I guess the only outcome from sending an email that wouldn't be bad to you is actually receiving a reply? That's understandable. But maybe "irrelevant" is a bit of a leap for you to make just because she hasn't read or has read but not responded to your email. She could be busy with other things right now. Or, to be honest, she could be like me and she could absolutely loathe emailing and have to psyche herself up to do it. I am currently a student, but at my last office job, I used to dread and procrastinate checking my email. Replying was no better. And it had absolutely nothing to do with my coworkers, or me not wanting to deal with them or whatever they needed from me, or anything like that. I just really don't enjoy emailing and kind of hate it, actually.