Simply replace the unfilled areas such as "" and "[date]" with your information.
It was a pleasure to meet with you to discuss opportunities within our firm. Unfortunately, we will not be able to offer you a position within the company at this time.
While your expertise and credentials were very strong, we had a selection of excellent candidates to choose from. Regrettably, we can only offer our position to one candidate. We must choose a candidate that best meets the unique criteria of this company.
Once again, we enjoyed meeting with you. We are thankful that you have taken an interest in our organization. We will keep your [application/resume] on file for a period of [number] [time interval] should another position become available for which you are better suited.