How do you write negative letter?

With the exception of a professional letter of condolence, all business correspondence (letters, memos, emails, etc.) should use positive terminology, even in the case of sending bad news. For example:

'We no longer carry that model' should say, 'We have replaced that model with the newer, more cost effective model...'

'We're sorry that the item was not received in time for...' should say, 'We are always striving to meet our customers' needs and encourage you to specify deadlines that are important for you...'

'We're returning the ... that you submitted because it does not meet our standards...' should say, 'Although your submission was not selected, we encourage you to continue your efforts to improve the (quality, design, script development, idea, etc.) of your...'