The Belt and Suspenders Man (1969)

Dudley, a hapless mailman bullied by a domineering wife, falls for a pretty young woman who comes to the post office every day hoping for a letter from her missing husband. Dudley discovers that her husband, a criminal, had been killed committing a robbery, but he feels so sorry for the woman that he begins writing letters to her pretending to be her dead husband. Complications ensue.