456, X Street, Y Avenue
[Subject: Normally bold, summarizes the intention of the letter] -Optional-
Dear ANDREW HALL,
I regret to inform you that I will not be able to schedule an appointment with you in the upcoming week for the discussion on your carrier options. I will be out of town due to business as you this is the most hectic time of the year. Call my secretary and fix another appointment. I shall be back by May 10. I look forward to seeing you.