Scams using the US Mail are rare. This is because unlike the Internet, the US Postal Service has armed agents (just like the IRS) to enforce the criminal statutes that apply to their service. Creating a physical piece of mailing and sending it through the mail creates a "paper" trail (literally) that gives the US Postal Service the ability to track the bad guys down. Read about the US Postal Inspection Service at https://en.wikipedia.org/wiki/United_States_Postal_Inspection_Service . Read about the IRS' armed agents at https://www.irs.gov/compliance/criminal-investigation/criminal-enforcement .
We have seen one purported scam letter. Although it used the IRS logo and copied many of the features of a real IRS letter, there was one telling giveaway. A real IRS letter will state that they have recalculated your tax due and give you two main choices:
(1) you agree with the IRS's conclusion and so will send them a check for the amount due, or
(2) you dispute the IRS' conclusion, and you reply with a description of why you filed the way you did and add any supporting documentation to support your case. You don't pay the IRS until you have had at least one chance to argue your case.
The scam letter said this: "pay us the amount due and if you dispute the amount, just pay us first, and we'll work it out later." Of course, the addresses are changed in the letter so that in any case, you send your money to the criminals.
Of course, if reading the letter still leaves you confused, please follow DoninGA's advice and contact the IRS and let the IRS agent help you understand the letter. As an alternative, you might try contacting Turbotax itself:
Did you purchase Audit Defense or MAX for those years? If so, we can tell you how to contact the company that handles that (intuit.taxaudit.com).
If you did not purchase Audit Defense/MAX, you can still get free help from TurboTax Audit Support Center. At the page linked below, click the blue "Get Help" button, and follow the prompts to get a phone number. It says "IRS letter", but they help with state letters, too.
https://support.turbotax.intuit.com/irs-notice/audit-support/
