How to respond to bigfoot letter

Your domain name does not appear to be yours. Take the letter seriously. Go to a PI lawyer today. The fine in nothing to joke about. That you did not do the due diligence before you registered is not an excuse nor a defense now.

Good luck.

Yours is likely a cease and desist letter or warning notice sent to you as a domain owner threatening legal action if domain name rights are not terminated within a specified period, usually 30 days.

There's no such thing as a $100K "fine." But as to whether their threats are real and they'll sue you and claim $100K in damages, it's a possibility. You don't mention who the source of this threat is, so it's not something anyone can know, but if the letter is from e.g., The Walt Disney Company, it's more likely to be a real threat.

You state you had no malice, and the domain name was available, but the questions about whether your use was in bad faith remain -- did you do any checking about anyone's trademark rights before you registered this domain name and set up this website? Does your website name and your website's products/services just happen to compete with theirs, and are consumers likely to be confused? If the answers are "no" and "yes," you're infringing on their trademark rights, and you'd better take their threats seriously.

See an IP litigator to fully disclose the facts of your situation.

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.

Q: "... are their threats real?"

R: No one can tell you w/o knowing the disputed domain name, who sent the letter, and what trademark or trade name rights are allegedly being harmed.

Q: "I didn't register the domain with any forethought of malice ..."

R: Interesting choice of words. Do a Google search for the terms "udrp" and "bad faith" and read a few of the discussions about the "bad faith" element of a domain name dispute proceeding. Knowing what is bad faith will help you register domain names in good faith.

Q: "Any thoughts?"

R: If your use of the disputed domain name is important to your business then you need to speak with a trademark attorney. If you're only warehousing the domain or monetizing it via a ppc site then you need to seriously consider simply turning it over to the trademark owner. Or you can fight this matter on principle -- which is sometimes not a bad tactic given that most domain name disputes are resolved via a UDRP action which requires each party to pay their own costs. Be warned however: the trademark owner can file a federal lawsuit under the Lanham Act which does, in some situations, requires the loser to pay the winner's costs.