A response letter provides the answers or information requested in a letter of inquiry. The objective is to satisfy the reader with an action that fulfills their request.
If you have neither the information requested nor the authority to reply, forward the inquiry on to the correct person. If you are the correct person, be prompt with your reply. Address every question courteously, even those that do not seem relevant.
Take into account that your reader may lack your expertise. Keep your response on point and avoid going beyond the scope of the reader's request.
When responding to a forwarded letter inform your reader in your opening paragraph that you are the correct contact person for all future communications. In your closing paragraph, express your willingness to be of further assistance.
In the sample response letter the writer acknowledges the reader's objective, provides requested information and promises a follow-up phone call.