I received a letter in the mail from the IRS the notice number is 4464C. What does that mean?

[bluedeb · Accepted solution]

It means the IRS has pulled your return for review but it is not an audit. They are verifying the information reported on your tax return and matching documents they received from payers such as employers, banks, etc. 

You can check the IRS website, Where's My Refund, for information about the processing of your  Federal return/refund.

https://www.irs.gov/refunds