Use the first paragraph to thank the reader. For example, if the reader was a job applicant that was not hired, the first sentence could state:
"Thank you for your application to XYZ. We had many qualified applicants and we gave your application careful consideration. As you are aware, there were only a handful of positions, therefore the hiring decision was that much more difficult."
If the reader is a vendor whose services you will no longer be using, a sentence such as this could be generated:
"We have enjoyed a positive and profitable working relationship between [reader's company name] and XYZ. Over the last ____ years, we have found your company to be a great help in fulfilling our clients’ needs. Your assistance has been invaluable."
For a reader that applied for credit with your company, the first sentence could read:
"Thank you for your recent application for credit with us. We thoroughly reviewed your application and gave it careful consideration."
The key to the first paragraph is to make the reader feel as if their time, service and patronage was appreciated.