http://www.irs.gov/irm/part21/irm_21-003-003.html

21.3.3.1.1 (10-02-2012)
Policy Statement P-21-3 (formerly P-6-12)

1. Policy Statement P-21-3 (formerly P-6-12) is the result of a team formed to review Corporate Critical Success Factor 61 which dealt with existing requirements for the quality and timeliness of responses issued by the Service.
2. A quality product or response is accurate, timely, and addresses all issues based on the information provided.
3. Responses must:
• Address all taxpayer issues
• Request additional information, if needed, from the taxpayer
• Notify the taxpayer if additional information is needed from outside the Service
• Be written in language the taxpayer can understand
4. See IRM 21.3.3.4.2, Policy Statement P-21-3 (Formerly P-6-12) Procedures.

21.3.3.3.4 (07-10-2014)
Quality and Timely Responses

1. Key terms are defined below:

A. A quality response is one that is timely, accurate, and professional. Based on information provided, a quality response resolves taxpayer's issues, requests additional information from him/her, or notifies him/her that we have requested information from outside the IRS.

B. A quality response must be written in language the taxpayers can understand.

C. Timely means that a final response or interim letter was initiated within 30 days of the IRS received date. However, when possible, you should try to initiate quality responses in less time.

2. For letters addressed to outside sources, reference the date of the incoming letter or inquiry and explain fully the action taken, even if it was exactly what the addressee requested.

3. Your final or interim letter response must read either . . . – "This is in response to your inquiry of" or "This is in response to your inquiry dated" ___. If the inquiry is a letter that is not dated, use the postmark date. If that date is unknown, use a date three days prior to IRS received date. If the inquiry is in the form of a fax, use the date the fax was transmitted to us. If inquiry is received from a Taxpayer Assistance Center use the IDRS received date. See IRM 21.5.1.4.2.4 , Received Date – Determination.

Exception:

If the closing action you take will generate a notice with a clear explanation to the taxpayer (for example, CP 210,CP 220, or CP 225, etc.), a final closing letter to the taxpayer is unnecessary.

4. See IRM 21.3.3.4.2.2, Interim Responses, for specific instructions regarding interim letters.

5. Required correspondence are quality and timely responses when responding to a taxpayer’s correspondence per Policy Statement P-21-3 (Formerly P-6-12). See also IRM 21.3.3.2, What is the Definition of Correspondence? - Policy Statement P-21-3 (Formerly P-6-12) Exclusion List. To ensure you are adhering to P-21-3 correspondence guidelines, check the following information before sending your closing letter:

A. The correct letter is selected.

B. The letter is addressed to the taxpayer or authorized representative.

C. Transcript of the account is included, if requested.

D. All applicable enclosures / attachments are included.

E. All necessary paragraph(s) are selected.

F. Correct paragraphs are selected.

G. Fill-in paragraph(s) addresses the taxpayer’s correspondence; includes appropriate, accurate, and complete information.

H. If the information required will not fit within the fill-in paragraph, select another paragraph that will provide the appropriate Information (e.g., when including balance due information).