There are, roughly speaking, two categories of businesses that receive this letter and differentiate themselves based off their response: 1) "Hobbyists" and th

There are, roughly speaking, two categories of businesses that receive this letter and differentiate themselves based off their response: 1) "Hobbyists" and the like who are not doing anything particularly valuable with the trademark and domain name. Even if these people can prevail in a lawsuit, the other company is hoping that the owner decides they can't (or won't) risk the time, money, and stress of going through a civil lawsuit. 2) People with valuable businesses whose rights are worth defending. The other company is already pretty sure you're not in this category, since you haven't vigorously defending your naming rights to date. Overall, you have prior use, and may be able to "win" if it gets to an actual lawsuit. The strength of your legal claim isn't the problem; if you have to spend high-five figures to keep the rights to your hobbyist website, you have already lost. Your goal is to convince these folks to leave you alone on as favorable terms as possible. If your domain name is not particularly valuable and important to you, this likely means A) hiring an attorney, B) using their services to convince the other company that you're in the second category, and then C) selling them your domain name for significantly more than it's worth to you. If your domain name is valuable to you, the only thing that changes is that you may need to pay the stochastic taxes that businesses have to pay to have access to the legal system for dispute resolution, and you might have a hilarious "thank you for informing us of your clients' violation of our trademark rights" demand letter sent back at them.