Question

how did the Postmaster become a changed man

Answer 1

The post master is described as an expressionless man in the story. He was irritated with Ali and even called him a pest. But when he heard the news of his sick daughter and waited for a night for further information about his daughter, he sympathizes for Ali who had been waiting for 5 years. What even saddened him was the letter for Ali after Ali's death. He became a changed person by being humble, and understood the non material value of a letter.

Hope this helps

Answer 2

The postermaster suffered as an anxious father when his daughter was lying ill in another town. Now he was able to understand a father's feelings. Moreover, his illusion of seeing coachman ali early morning made him confused. This resulted in his change.