First paragraph needs to be introduced with your name and the reason why you have written the letter. The purpose of the letter and its possible implication from the facts received by the reader should also be highlighted so that the reader better understands it at the very first sight. There needs to be a good communication so that the reader is able to provide the necessary details without any hidden facts along with possible further requirement about the inquiry.
Following the first paragraph, you need to have some kind of inputs into second paragraph so that you make a point for your necessity for that inquiry. Also, make sure that you have demanded such because of the fact that it is the pre-requisite for any further action.
At last paragraph, you need to highlight the importance of the reader’s dedicated contribution towards its efforts for responding. There needs to mention positive respond from the reader.