Thanks for the advise Nihill...
It's just that, I tried calling one of the tracer services to inquire and they told me that they can trace the source of the IP address of the one opening my email, once they put a tracker of some sort when I buy their services. In addition, they told me that they can search/trace back if they can, but it will be more expensive. The cheaper sevices are the ones that they can put a monitor for future log-ins.

In another question, is it easy to inquire from big ISP providers such as AOL, if the source is a dial-up connection? I tried tracing an IP source, on WHOIS and it gave me packets. What are they? Please let me know.