Inquiry letter is written to request for getting the information from the reader. The objective of the letter is to get the response from the reader in regards to the inquiry.
While inquiring enough information should be provided to the reader so that the response you get is beneficial. The letter should be written to the person from where you get the positive response.
Make list of points that you need to inquire and put in sequential order, this will help the reader.
The queries must be sent in crystal-clear language that avoids undue confusion for the reader. The letter should be supported by a strong reference that would further enhance the speed of processing the inquiry.