Original sentence: Acceptance letter.Acknowledgment letter.Adjustment letter.Announcement letter.Apology letter.Appeal letter.Appointment letter.Appreciation letter.Approval letter.Authorization letter.Cancellation letter.Claim letter.Compliment letter.Confirmation letter.Farewell letter.Follow up letter.Goodbye letter.Inquiry letter.Marketing letter.Notification letter.Recommendation letter.Referral letter.Refusal letter.Rejection  letter.Reminder letter.Request letter.Response letter.Retirement letter.Sponsorship letter.Suggestion letter.Sympathy letter.Termination letter.Verification letter.Welcome letter