The Washington Collection Agency Act requires collection agencies who operate in Washington to be licensed in Washington, but it does not to my knowledge require a presence in Washington. There is at least one large collection law firm in Oregon that does this.
This answer is in the nature of a general legal analysis and is not tailored to the facts of your specific situation. It should not be construed as legal advice, and you should meet with an attorney before taking action on this matter.
There might be some other issues here with the lawyer reaching across state lines to collect a debt. I'd be happy to look at the letter ad give you some free advise afterwards. Further, I know a great lawyer in Washington if I think the letter is actionable. Seems dangerous for me for a law firm to be collecting in debts in states they are not licensed to practice.
I am an attorney licensed to practice law in Ohio and some Federal Courts throughout the United States. I am not answering your question to solicit you as a client and there is a good chance that I am not licensed to practice law in the state that you reside. I hope that you find my assistance beneficial and, at most, use my advise as a finger pointing in the right direction. An attorney client relationship is not established by posting back and forth online. One of the most beneficial aspects of working with an attorney is the attorney client privilege which does not exist when you post personal facts online to faceless strangers. Hire an attorney if you want specific legal advise. If you cannot afford one, call your local bar association or search "(your city) legal aid" online. The fact that you took the time to post your question online likely means that you could use the aid of an attorney. Call around your area and see if any local attorneys offer free consultations.
I think Mt. Hyslip is correct. If the collector has no ability or intention of filing suit against you then you may have an FDCPA claim against them. If the collector is not licensed to practice law in your state, that might be the case. You should speak to a competent consumer lawyer in your area. If Mr. Hyslip has a name, I would call that lawyer. It typically costs nothing to see if you have a claim.