^ I was about to suggest a tracking pixel or image like grav6. I am sure that there are tons of places to track an image with various free analytics. I use piwik to do it all the time, but you have to install that on a server. If the person is hiding from you though... good luck. I've been through that before. If you find out they opened the email though, it doesn't really put you any further ahead, it just confirms that they are dodging you.
If you don't mind me asking, what is it you are needing and what consequences are you facing? No need to answer that if you don't want to, just curious as I am sure others are.
Firstly, I just wished to thank all who responded. You've all given me a bit of advice that I will not let go to waste.
Now, as for what this is all about... basically, and this is pretty sad...
Sob story goes like this: I've not had full-time work in nearly 7 months, and I've not had this happen since I started working at the age of 16. Anyway, saying more than I need to really. A came to a friend with an idea to get him up in Google, which worked, apparently. It's nothing new. Simply put: Create email accounts, he paid me $5 each. What I needed to do was create the accounts (which I outsourced to friends at $2 per email), then I used these gmail accounts along with the youtube channels, which I made "band channels", added the needed info in the channel profile, ie URL, and on quite a few of his videos, he made first page and held it, within about a day on some. The videos I made were pretty well done, too. I matched the music with his niche, etc. Its all fairly simplistic, I know. But it did work, 100%.
That was, believe it or not, my main source of income for at least 3 months. I would make upwards of 80 accounts per week. All verified.
Sorry for the tl;dr. Im just not used to having to worry so much about work, cos I have always worked hard, mainly tile install/masonry. All this is new to me, as of just 2 months ago. Also, I just now realized I made within the 4th spot in my location for some very , very good keywords. :3
That is why I am here. Some I have learned from this site, with the plethora of information available. I'm just desperate to make something work here, with something. Also, I made today more in a few hours with AdSense than I have all month. Sadly, being so stressed and unable to focus due to all this, my site(s) are in a bad state. They look like rubbish, most of everything is not done right. So I am basically just winging it right now until , I am praying, this person turns up and lets me know that he didnt mean to avoid me. Highly dount it, considering even when I send him a text via email, it comes back saying cant be delivered, and his cell phone says he is not accepting calls. Guess thats that.