An IRS Form 5564 should be mailed to the address shown on the IRS notice that came with the form. IRS Form 5564 is called a Notice of Deficiency and should be returned with payment if the taxpayer who received it agrees with the charges proposed by the IRS.
If the individual to whom the letter was addressed does not agree with the proposed changes, Form 5564 does not need to be returned. Instead, the taxpayer can file a petition with the U.S. Tax Court by the date listed on the notice. If there is any other information the IRS should review related to the notice, it should also be sent to the address specified. If the date listed on the notice has passed, it is too late make an appeal and charges must be paid.