For gods sake whatever you do don't answer that letter. It is another of those internet scams. Usually these people are from Africa or other countires where our government can't touch them and they know it. I get something like that everyday and sometimes several a day. I need to change my email address to get rid of that crap. Once they get your info from you they will steal your identity and all the money you have in an account that you give the info to and more and you will live a life of nightmares. I also got this a month ago, It was for $182.00. I reported it to our local tv stations and they investigated it and told us that the IRS does NOT ask for that info and if you have that money coming they will automatically send it to you. That also happened to me, the IRS owed me almost $3000.00 and they sent me a check in the mail unbeknownist to me I got this check in the mail one day. There was no notice. I am just telling you this to let you know how the system works.
In your case if you haven't filed for all these years , the only letter they would send you is a warning letter but they don't even do that.