With the exception of ________,all of the following guidelines can help you close a negative message on a respectful note.

A) being sincere
B) managing future correspondence
C) avoiding an uncertain conclusion
D) promising an optimistic future outcome

The best choice is option D (promising an optimistic future outcome) as it is the only guideline that does not help to close a negative message on a respectful note. It may come across as insincere or unrealistic if the negative situation is unlikely to have a positive outcome in the near future. Options A, B, and C all help to close a negative message respectfully by expressing sincerity, managing future correspondence, and avoiding an uncertain conclusion, respectively.