what is CP21C NOTICE LETTER FROM THE IRS?

It's an assessment notice. You probably filed your 1040 and didn't send them the payment of tax liability due. Read it closely. The notice will explain why they sent it and what you need to do to rectify the situation. Above all, don't panic. Read it carefully. If you disagree with them, there is usually a phone number to call or an address to write to. Be sure you include your SSN and any other information from the notice in your letter so they know what the letter is in reference to.

Good luck! :)

I believe the best thing to do is read your notice closely and if you don't understand it then you should call phone number provided. Or take your notice with you to the local IRS office in your city.

Tax adjustment was made to return, resulting in a overpayment of $1 or more.

Reason for Issuance: We send a CP 21 when tax changes are made to account resulting in a overpayment of $1 or more and you are due money back.