A letter of inquiry asks for more information regarding a certain product or service. Inquiry letters are of two kinds: solicited and unsolicited.
When a product is advertised in a local newspaper and you want additional information on the product or service and you write to the company, you are writing a solicited letter of inquiry. You were prompted to write to the company or person.
When you happen to read a column and you want to ask more information form the author, that is a unsolicited letter. The columnist did not prompt you to write him or her.
In the first part of your letter when it is solicited, mention the advertisement you saw. It would be helpful you include the date it appeared on the paper. When it is unsolicited, introduce your self first then cite the date and publication you read the columnist's work.
Then explain why you sent that letter, what is your reason for writing, before mentioning the information you need.
For solicited letters, express your thanks for the help that is given. When it is unsolicited, offer to pay the mailing cost if you requested additional materials or what.
Acknowledge that inconvenience you have bought to them and end that you are hoping for a positive reply.
This is the way you should write your inquiry letters. There are other several samples you can check out online.
Comments