Legality of a Registered Domain Name

Most state laws provide little or no trademark protection for "descriptive" or "generic" trade names. However, the policy underlying trademark protection is to avoid consumer confusion while not conferring on one entity or person monopoly rights in a name that would limit competition in a general category of goods or services. It would seem to me that you as a mason county realtor could own and use the website. Would Board of Mason County Realtors Association also object to your using the words "I am a Mason County Realtor" in a print ad?

If not, then BOMCRA cannot claim that your use of the website infringes something in which it owns.

Similarly, one company cannot own the phrase: Mason County Spaghetti House as this would foreclose other spaghetti houses from advertising. This would stifle competition and the spaghetti in Mason County would never get better.

What is it that BOMCRA says your domain name is in violation of? Do they have a BOMCRA trademark, or a MCRA or MCR trademark? You haven't mentioned the specifics of their claim, other than their sense of victimization because of your competition with them.

If they want your domain name and you refuse to give it up voluntarily, they have to file a claim known as UDRP, Uniform Domain-Name Dispute-Resolution Policy, a process established by the Internet Corporation for Assigned Names and Numbers (ICANN). They have to prove 3 things to win: (1)
Your domain name is identical or confusingly similar to a trademark or service mark in which they have rights; (2) you have no rights or legitimate interests in the domain name; and (3) you registered the domain name and are using it in "bad faith."

It's not clear whether anyone has registered any trademarks, or how long each of you has been using "MCR" but as my colleague has pointed out, that's a description that every realtor in MC can lay claim to. Further, it seems quite unlikely that the BOMCRA could win a proceeding to take your domain name from you. You have as legitimate interest as they do in the domain name and you're not using it in bad faith.

If they follow up with a case and desist letter, you'll need to hire an IP lawyer to respond for you regarding the domain name and whatever trademark issues are also present.

Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.