Velocity Reviews - Read Notify questions

I sent an email reply that included all of the original recipients of the incoming email and a bit later checked my email again and had a message from REadNotify saying my reply had not been sent because I wasn't registered with ReadNotify. Until today, I had never heard of this company, and after googling the company name, I found a thread on this site, so I thought I'd come here and ask if anyone can tell me why I got this notification out of the blue, and if in fact, my reply was or was not sent at all. After reading a bit more about what the company does, I am probably not at all interested in using the service, how do I stop this from happening again? BTW I am not a computer techie, I am just a garden-variety email user, yahoo, specifically.
Thanks for whatever you can offer. 8)