The postscript often contains the thought that finally escaped the letter’s good manners.

The real message often waits until the form is over. Once the letter has done its polite work and signed itself off, the guard drops, and the thing that was pressing all along slips out below the line where it does not have to be organized. Manners keep certain truths out of the main body.

Listen for the postscript in person: the remark at the door, the line dropped as the call is ending, the aside after the meeting formally closes. That is frequently where the actual concern lives. If you hear one, do not let it pass as a throwaway, because the person may have needed the exit to be able to say it.