Got email from Turbotax pertaining to 2015/2016 reg. sales tax. Does it mean I can amend those return if I forgot to report sales tax on something I purchased?

We don't know what emails have been sent.  Maybe you could paste a copy here for us to review (without your name, of course).

That doesn’t sound like something Turbo Tax would send out especially for old years.  Who exactly is the sender?  

This email is being sent out because there was a TurboTax defect/bug that originated in 2014 but also affects 2015 and 2016.  They don't mention 2104 because you can't post an amendment for 2014 and they don't want you to know that you have lost part of your refund due to a mistake on their side.

Hi chall2022,

Please read this article for more information.

Amending Your 2015 and 2016 Federal Tax Returns to Claim State Sales Tax Deduction

Thank you for posting this link.  To add to it, TurboTax is skirting around that this is due to a bug in their solution.  It also affected 2014 but they don't mention this since you can't file an amendment for 2014 since it is outside of the IRS 3 year limit.  I would recommend looking for a different solution to Turbotax since this is the core function of what TurboTax is supposed to do with complete confidence.