First off I am not a lawyer so contacting one that understands internet laws is always useful and don't take my advice as legal advice. A web patent lawyer might be what you need.
That being said, my company has received a number of these emails as well and we are in the US. Usually, if you Google the email address, company name, or some other piece of info about the email you will see a number of sites stating that the email is a scam. China as far as I know has little to no intellectual property laws.
Furthermore, if your domain does not have a TLD that belongs to China, I would assume a Chinese company has no legal rights whatsoever to do anything about your site name. Wikipedia has a list of all of the TLDs, http://en.wikipedia.org/wiki/List_of_Internet_top-level_domains, China has a couple because of their numerous special districts.